Abstract
Let U be a sequence of positive integers which grows essentially as a geometric progression. We give a criterion on U in terms of its distribution modulo d, d = 1, 2, …, under which the set of positive integers expressible by the sum of a prime number and an element of U has a positive lower density. This criterion is then checked for some second order linear recurrence sequences. It follows, for instance, that the set of positive integers of the form \(p + \left\lfloor {(2 + \sqrt 3 )^n } \right\rfloor \), where p is a prime number and n is a positive integer, has a positive lower density. This generalizes a recent result of Enoch Lee. In passing, we show that the periods of linear recurrence sequences of order m modulo a prime number p cannot be “too small” for most prime numbers p.
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Dubickas, A. Sums of primes and quadratic linear recurrence sequences. Acta. Math. Sin.-English Ser. 29, 2251–2260 (2013). https://doi.org/10.1007/s10114-013-1059-x
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DOI: https://doi.org/10.1007/s10114-013-1059-x