OFFSET
1,6
COMMENTS
Also number of divisors of 5*n-2 of form 5*k+4.
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..10000
FORMULA
MATHEMATICA
a[n_] := DivisorSum[5*n-2, 1 &, Mod[#, 5] == 2 &]; Array[a, 100] (* Amiram Eldar, Aug 16 2023 *)
PROG
(PARI) a(n) = sumdiv(5*n-2, d, d%5==2);
(PARI) a(n) = sumdiv(5*n-2, d, d%5==4);
(PARI) my(N=100, x='x+O('x^N)); concat(0, Vec(sum(k=1, N, x^(2*k)/(1-x^(5*k-1)))))
(PARI) my(N=100, x='x+O('x^N)); concat(0, Vec(sum(k=1, N, x^(4*k-2)/(1-x^(5*k-3)))))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Dec 23 2022
STATUS
approved