The Ramanujan Journal

, Volume 6, Issue 4, pp 469–490 | Cite as

Sums of Five, Seven and Nine Squares

  • Shaun Cooper

Abstract

Let rk(n) denote the number of representations of an integer n as a sum of k squares. We prove that
$$\begin{gathered} r_5 \left( n \right) = r_5 \left( {n\prime } \right)\left[ {\frac{{2^{3\left\lfloor {\lambda /2} \right\rfloor + 3} - 1}}{{2^3 - 1}} - \varepsilon _5 \left( {n\prime } \right)\frac{{2^{3\left\lfloor {\lambda /2} \right\rfloor } - 1}}{{2^3 - 1}}} \right] \hfill \\ {\text{ }} \times \mathop \prod \limits_p \left[ {\frac{{p^{3\left\lfloor {\lambda p/2} \right\rfloor + 3} - 1}}{{p^3 - 1}} - p\left( {\frac{{n\prime }}{p}} \right)\frac{{p^{3\left\lfloor {\lambda p/2} \right\rfloor } - 1}}{{p^3 - 1}}} \right], \hfill \\ \end{gathered}$$
where
$$\varepsilon _5 \left( {n\prime } \right) = \left\{ \begin{gathered} {\text{0 if }}n\prime \equiv 1 \left( {\bmod {\text{ }}8} \right) \hfill \\ 4{\text{ if }}n\prime \equiv 2{\text{ or 3 }}\left( {\bmod {\text{ 4}}} \right) \hfill \\ 16/7{\text{ if }}n\prime \equiv 5{\text{ }}\left( {\bmod {\text{ 8}}} \right). \hfill \\ \end{gathered} \right.$$
Here n = 2λppλp is the prime factorisation of n, n′ is the square-free part of n, the products are taken over the odd primes p, and (\(\frac{n}{p}\)) is the Legendre symbol.

Some similar formulas for r7(n) and r9(n) are also proved.

Hecke operator modular forms of half integer weight sums of squares 

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Copyright information

© Kluwer Academic Publishers 2002

Authors and Affiliations

  • Shaun Cooper
    • 1
  1. 1.Institute of Information and Mathematical SciencesMassey University—AlbanyAucklandNew Zealand

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