A103638 a(n) = Sum_{d|n, d==2 mod 3} d^2.

0, 4, 0, 4, 25, 4, 0, 68, 0, 29, 121, 4, 0, 200, 25, 68, 289, 4, 0, 429, 0, 125, 529, 68, 25, 680, 0, 200, 841, 29, 0, 1092, 121, 293, 1250, 4, 0, 1448, 0, 493, 1681, 200, 0, 2061, 25, 533, 2209, 68, 0, 2529, 289, 680, 2809, 4, 146, 3400, 0, 845, 3481, 429, 0, 3848

Offset: 1

Author

Ralf Stephan, Feb 11 2005

Keywords

• nonn

Links

• Seiichi Manyama, Table of n, a(n) for n = 1..10000

Programs

Mathematica

a[n_] := DivisorSum[n, #^2 &, Mod[#, 3] == 2 &]; Array[a, 100] (* Amiram Eldar, Jun 30 2023 *)

PARI

a(n) = sumdiv(n, d, (d%3==2)*d^2); \\ Seiichi Manyama, Jun 30 2023