Abstract
Nowhere in mathematics is the progress resulting from the advent of computers as apparent as in the additive number theory. In this part, we describe the role of computers in the investigation of the oldest function studied in mathematics, the divisor sum. The disciples of Pythagoras started to systematically explore its behavior more than 2500 years ago. A description of the trajectories of this function—perfect numbers, amicable numbers, sociable numbers, and the like—constitute the contents of several problems stated over 2500 years ago, which still seem completely impenetrable. The theorem of Euclid and Euler reduces classification of even perfect numbers to Mersenne primes. After 1914 not a single new Mersenne prime was ever produced by hand, and since 1952 all of them have been discovered by computers. Using computers, now we construct hundreds or thousands times more new amicable pairs daily than were constructed by human beings over several millennia. At the end of the paper, we discuss yet another problem posed by Catalan and Dickson.
Notes
I deliberately do not indicate the exact value: today, hundreds of thousands of new such pairs are discovered every day, and so the exact number of known pairs is likely to change simply over the period of editorial preparation of this article.
Stewart [327] put the question differently, “do dice play God”?
In fact, Thomas Nicely discovered the FDIV bug in 1994 while calculating the Brun constant, the sum of reciprocals of simple twins.
I cannot resist quoting the following illustrative fragment from Robert Juricevic’s review of this book: “It seems that we will only begin to seriously understand the sequence of prime numbers when we are freely able to work with prime numbers which are at least 1 million digits in length. It would certainly be fantastic to discover a trick to do arithmetic with such huge fundamental building numbers without the aid of a computing machine. It would also be nice to be able to fly without the aid of a flying machine. Plainly, the computer is an indispensable tool to the theoretical mathematician studying the sequence of prime numbers, as well as to the mathematician applying prime number theory in industry”—“If only I could have such feathers, and such wings ….”
“Multiply 2 071 723\(~ \cdot \)5 363 222 357 by hand. Feel the joy.”
“There is much pleasure to be gained from useless knowledge.”
Constance Reed is the sister of Julia Robinson.
Formally, the book Trattato de Numeri Perfetti [57] containing these results was published in 1603. However, its first sentence is “Nel trattato dè numeri perfetti, che giàsino dell’anno 1588 composi, ….” On p. 40, a table of all prime numbers \(p < 750\) is reproduced. Since \({{727}^{2}} = 528{\kern 1pt} 529 > {{M}_{{19}}}\), without even particularly delving in the text, it is clear how exactly Cataldi acted. He tested as possible divisors of \({{M}_{{13}}}\), \({{M}_{{17}}}\), and \({{M}_{{19}}}\) all primes not exceeding the integer part of their square roots—“sua prossima radice quadra.” It is beyond belief that Cataldi could extend this kind of direct calculation to \({{2897}^{2}} = 8\,392\,609 > {{M}_{{23}}}\).
In accordance with the custom of the time, he says “any prescribed amount.”
Both of these text fragments are reproduced in full in Latin in an article by Walter William Rose Ball [310], where they are, of course, somewhat easier to read than in the original 17th-century edition. The last sentence of this paragraph in the original reads as follows: “agnoscere num dati numeri 15, aut 20 caracteribus constantes, sint primi necne, cùm nequidem saeculum integrum huic examini, quocumque modo hactenus cognito, sufficiat.” Rose Ball concludes from this, “From the last clause it would appear that he did not know how the result was demonstrated.”
Clearly, this text refers to Paul Tannery, who at about this time was preparing editions of the works of Fermat and Descartes, not to his brother Jules Tannery.
“… valeurs qu’il tenait, supposent certains, de Fermat lui-même” [274].
Derrick Henry Lehmer (1905–1991), husband of Emma Markovna Lehmer (1906–2007), who should not be confused with his father Derrick Norton Lehmer (1867–1938), also a professor at the University of California at Berkeley, who also studied exactly the same kind of number theory. However, they are not systematically distinguished by the main databases: in MatSciNet, the works of D.N. Lehmer’s are not classified as such, but in ZBMath they are attributed to D.H. Lehmer. Therefore, the only way to differentiate them is to look at the texts of the articles themselves. The generalizations of perfect numbers mentioned below are D.N. Lehmer. However, in this case, we are talking about the works of D.H. Lehmer, which consituted the contents of his PhD in 1930.
The village priest Ivan Pervushin was the eldest of 17 children in his family, which from childhood aroused his interest in prime numbers. However, Wikipedia claims that there were only 16 children in the family of his parents, which, of course, would explain his interest in powers of 2. Before the discovery of the Mersenne prime \({{M}_{{61}}}\) in 1877, he found a prime divisor of Fermat’s number \({{F}_{{12}}}\), and in 1878 the Fermat number \({{F}_{{23}}}\). Before him, only Euler and Clausen could find new divisors for Fermat numbers, and, simultaneously with him, Lucas.
As the reviewer noted, in a situation where there are 17 children in a family, interest in prime numbers should arise in the junior child. The author missed this obvious consideration.
I could not find Pervushin’s original publication, but only a mention of his findings in the Bulletin of the Petersburg Academy. A picturesque fragment from the report of Imshenetsky and Bunyakovsky is that “Tout en laissant à la charge de l’auteur la responsabilité pour l’exactitude du résultat qu’il a obtenu au bout de ses longs et fatigants calculs,—nous devons constater, pour sauvegarder son droit de priorité, que 1°. Le manuscrit du père Pervouchine contenant sa communication de l’année 1883, est déposé aux Archives de notre Académie; ce document est accompagné de quelques tables, calculés par l’auteur, et destinés a faciliter la vérification du résultat qu’il a obtenu” [178].
“In addition, there was another article (Catalan) on this issue, but, unfortunately, I was deprived of the opportunity to get acquainted with this article, since I could not get this journal anywhere in Moscow” [11].
We reproduce Powers’ obituary written by Lehmer for AMS, which mentions both of these circumstances: “This amateur mathematician died on Jan. 31, 1952, at Puente, California. He would have been 77 years old on April 27. Mr. Powers was more responsible than any other man for the demonstration of the failure of Mersenne’s conjecture. He proved that \({{2}^{{89}}} - 1\) and \({{2}^{{107}}} - 1\) were primes, and that several other Mersenne numbers were composite by long and laborious desk machine calculations. He was not aware of the discovery, the night before his death, of two new Mersenne primes (MTAC, vol. 6, p. 61). Mr. Powers was born in Fountain, Colorado, and spent most of his life in Denver.”
The same Raphael Robinson, the famous logician and husband of Julia Robinson.
The same Hans Riesel, who is known for his work on the factorization of numbers of the form \(k \cdot {{2}^{n}} \pm 1\): the Lucas–Lehmer–Riesel test, Riesel numbers, Riesel Sieve, etc.
Noll has since continued to deal with factorizations; on his webpage (http://www.isthe.com/chongo/index.html) you can find interesting links on this matter.
Imagine how much a month of running such a machine would cost at that time—I have hypotheses about how schoolchildren could get access to it, but I am embarrassed to utter them.
See the official website https://www.mersenne.org/; the project name is pronounced gimps.
I do not know if this was originally meant, but Prime95 has become a favorite tool for testing system stability: “Prime95 has been a popular choice for stress/torture testing a CPU since its introduction, especially with overclockers and system builders. Since the software makes heavy use of the processor’s integer and floating point instructions, it feeds the processor a consistent and verifiable workload to test the stability of the CPU and the L1/L2/L3 processor cache. Additionally, it uses all of the cores of a multi-CPU/multi-core system to ensure a high-load stress test environment.”
Exaflops = quintillion = million million million floating point operations per second.
A well-known historical anecdote is connected with this decomposition. At the meeting of the American Mathematical Society on October 31, 1903, Cole gave a lecture, during which he did not utter a single word, but simply multiplied 193 707 721 by 761 838 257 287 on the board. He later mentioned that it took him “three years of Sundays” to find these divisors.
This is without even discussing the question which of the historical calculations were checked or repeated, how many errors there were, etc. “And that leaves five—Well, six actually. But the idea is the important thing!”
Mathematica 11.3 on an HP EliteBook 830GS with an Intel Core i7-8550U 1.99-GHz processor.
However, some believe that the first irreproachable primality proof of \({{M}_{{127}}}\) was given only in 1894 by Fauquembergue, but even in this case the record stood for 57 years! I do not make any judgments about this, but many authors still have great doubts about the calculations of Fauquembergue himself (see, for example, [167]).
The only source known to me where the opinion is seriously expressed that the number of Mersenne primes is finite is an article by Golubev [131].
In fact, this is a later reinterpretation. Catalan himself is much more careful: “Si l’on admet ces deux propositions, et si l’on observe que \({{2}^{2}} - 1\), \({{2}^{3}} - 1\), \({{2}^{7}} - 1\) sont aussi des nombres premiers, on a ce théoréme empirique: Jusqu’une certaine limite, si \({{2}^{n}} - 1\) est un nombre premier p, \({{2}^{p}} - 1\) est un nombre premier \(p'\), \({{2}^{{p'}}} - 1\) est un nombre premier \(p''\), etc. Cette proposition a quelque analogie avec le théoréme suivant, énoncé par Fermat, et dont Euler a montré l’inexactitude: Si n est une puissance de \(2\), \({{2}^{n}} + 1\) est un nombre premier.” Comparing this conjecture with Fermat’s conjecture that the Fermat numbers are prime, he directly hints that it may be wrong already at the next step (cf. [114, 132]).
“Haec autem propter senarii numeri perfectionem eodem die sexiens repetito sex diebus perfecta narrantur, non quia Deo fuerit necessaria mora temporum, quasi qui non potuerit creare omnia simul, quae deinceps congruis motibus peragerent tempora; sed quia per senarium numerum est operam significata perfectio. Numerus quippe senarius primus completur suis partibus, id est sexta sui parte et tertia et dimidia, quae sunt unum et duo et tria, quae in summam ducta sex fiunt,” XI–XXX.
Seeing these numbers in such a context, any specialist in exceptional numerology cannot help but start. After all, in fact, 56 = 2 · 28 is the dimension of the smallest representation of E7, and 248 = 496/2 is the dimension of the smallest representation of E8.
To avoid doubt, I specify that this is Benjamin Peirce, 1809–1880, father of Charles Peirce, 1839–1914. In Russian, they usually shamelessly write “Pierce.”
That Sylvester! In his old age, he suddenly began to experiment with the classical impenetrable problems of number theory, including Goldbach’s problem.
The same Gradshtein, better known to Soviet mathematicians as Gradshtein–Ryzhik.
More under some additional assumptions.
I first heard about multiple perfect numbers from Nikolai Grigoryevich Chudakov in 1968. Then, at LOMI, and even in the Mathematics and Mechanics Faculty, letters from lovers of mathematics with new great discoveries came in a stream. They were written by hand on checkered pieces of paper torn from school notebooks. About 90% of those were proofs of Fermat’s theorem with the same standard error. But there were also more interesting things—a refutation of the Cantor diagonal process, a proof of the even Goldbach conjecture based on the equality 3 + 3 = 5, a proof of the formula (–1) ⋅ (–1) = –1, etc. Now, of course, all such delirium immediately spills into social networks, bypassing the Science Department of the Vasileostrovsky district committee of the CPSU (in fact, social networks now play the same role). So, Chudakov mentioned the letter, whose author found a general solution to the equation \(\sigma (n) = kn\) for any k and assured that this knowledge guarantees immortality in the literal physical sense: “Some pirates achieved immortality by great deeds of cruelty or derring-do … But the captain had long ago decided that he would, on the whole, prefer to achieve immortality by not dying.” Nikolai Grigorievich smiled and added: “This is not surprising, because already the one who finds all the solutions to the equation \(\sigma (n) = 2n\) will become immortal.” Much more about the role of Nikolai Grigorievich in the emergence of this article, as well as about how to avoid Thanatos and black Kera, is narrated in [379].
The term “friendly pair” also exists, but it means something completely different, equality σ(m)/m = σ(n)/n.
This view is widely accepted in the literature: “It might be argued that elementary number theory began with Pythagoras, who noted two-and-a-half millennia ago that 220 and 284 form an amicable pair.” [262].
“Two hundred goats, twenty goats, two hundred sheep, twenty rams,” Genesis, XXXII, 14.
Herman te Riele writes about this that “De meeste bekende bevriende getallenparen zijn gevonden met behulp van variaties van de Regel van Thabit ibn Kurrah” [674].
Another Paganini, full namesake.
However, Lee claims that Escott made mistakes and in fact discovered only 219 pairs.
Here, however, one must carefully compare how they take into account repetitions, Iranian and Arabic authors, etc. But this, of course, is for a serious proper historical work.
To illustrate what kind of nonsense the Internet is filled with, I will quote a tale about Fedor Ivanovich Duz-Khotimirsky, which was widely discussed on chess sites: he “… filled entire reams of paper with numbers, revealing ‘related numbers,’ … And mathematical geniuses sat in academies, and to one of them, an academician named Vinogradov, Uncle Fedya sent the ‘related numbers’ he had discovered in infinity. As I understand it, Descartes found the first 14 of these numbers in his time, and Uncle Fedya brought their number to 600. The academician, of course, was an intelligent person and published Duz’s discovery under his great name. Duz was terribly angry with him, but he did not sue and prove his authorship. Firstly, because he would have lost for sure. And secondly, because he did not want to appeal to the state, which he did not recognize in principle” [9]. Wow, six hundred pairs of amicable numbers by hand in a school notebook—this is a stronger joke than Goethe’s Micromegas.
“Millionen stehen hinter mir.”
We do not consider triples with repeating elements.
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ACKNOWLEDGMENTS
I owe many thanks to Vladimir Khalin, with whom I started this whole affair 15–20 years ago, and to Aleksandr Yurkov, who breathed new life into it. I give special thanks to Sergei Pozdnyakov, who convinced me to write this series of articles. I had very useful discussions with Galina Ivanovna Sinkevich, which influenced the content of the last sections. I am indebted to Boris Kunyavsky, Aleksei Stepanov, and Ilya Shkredov, who read the first draft of this article with great care and suggested a large number of corrections and improvements.
Funding
The study was financially supported by the Russian Foundation for Basic Research within the framework of the scientific project no. 19-29-14141 “Studying the Relationship between Conceptual Mathematical Concepts and Their Digital Representations and Meanings As the Basis for Transformation of School Mathematical Education.”
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Vavilov, N.A. Computers As a Novel Mathematical Reality: III. Mersenne Numbers and Sums of Divisors. Dokl. Math. 107, 173–204 (2023). https://doi.org/10.1134/S1064562423700783
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DOI: https://doi.org/10.1134/S1064562423700783