OFFSET
1,6
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = A001842(4*n-3).
G.f.: Sum_{k>0} x^(3*k)/(1 - x^(4*k-1)).
MATHEMATICA
a[n_] := DivisorSum[4*n-3, 1 &, Mod[#, 4] == 3 &]; Array[a, 100] (* Amiram Eldar, Aug 23 2023 *)
PROG
(PARI) a(n) = sumdiv(4*n-3, d, d%4==3);
(PARI) my(N=100, x='x+O('x^N)); concat([0, 0], Vec(sum(k=1, N, x^(3*k)/(1-x^(4*k-1)))))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Dec 22 2022
STATUS
approved