A229296 - OEIS

The OEIS is supported by the many generous donors to the OEIS Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give

A229296

Number of solutions to x^2 + y^2 == n (mod 2*n) for x,y in [0, 2*n).

2, 4, 2, 8, 18, 4, 2, 16, 18, 36, 2, 8, 50, 4, 18, 32, 66, 36, 2, 72, 2, 4, 2, 16, 130, 100, 18, 8, 114, 36, 2, 64, 2, 132, 18, 72, 146, 4, 50, 144, 162, 4, 2, 8, 162, 4, 2, 32, 98, 260, 66, 200, 210, 36, 18, 16, 2, 228, 2, 72, 242, 4, 18, 128, 450, 4, 2

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

LINKS

Andrew Howroyd, Table of n, a(n) for n = 1..1000

FORMULA

a(n) = 2*A086933(n). - Andrew Howroyd, Aug 07 2018

MATHEMATICA

A[n_] := Sum[If[Mod[a^2+b^2, 2n] == n, 1, 0], {a, 0, 2n - 1}, {b, 0, 2n - 1}]; Array[A, 100]

PROG

(PARI) a(n)={my(m=2*n); my(p=Mod(sum(i=0, m-1, x^(i^2%m)), x^m-1)^2); polcoeff( lift(p), n)} \\ Andrew Howroyd, Aug 07 2018

CROSSREFS