A364097 - OEIS

%I #12 Jul 12 2023 01:01:04

%S 1,1,1,3,1,1,4,1,1,7,1,1,6,1,1,9,1,4,8,1,1,11,1,1,10,5,1,13,4,1,12,1,

%T 1,20,1,1,14,1,1,20,1,11,16,1,1,19,1,1,18,8,4,21,1,1,25,1,1,35,1,1,22,

%U 4,1,25,1,10,24,7,1,27,1,1,29,15,1,34,1,1,28,1,8,42,1,4,30,1,1,33,1,17,32,1,1

%N Expansion of Sum_{k>0} k * x^(3*k-2) / (1 - x^(5*k-4)).

%F a(n) = (1/5) * Sum_{d | 5*n-2, d==1 (mod 5)} (d+4).

%F G.f.: Sum_{k>0} x^k / (1 - x^(5*k-2))^2.

%t a[n_] := DivisorSum[5*n - 2, # + 4 &, Mod[#, 5] == 1 &]/5; Array[a, 100] (* _Amiram Eldar_, Jul 12 2023 *)

%o (PARI) a(n) = sumdiv(5*n-2, d, (d%5==1)*(d+4))/5;

%Y Cf. A359236, A364093.

%K nonn

%O 1,4

%A _Seiichi Manyama_, Jul 04 2023