A363030 - OEIS

%I #14 Jul 06 2023 07:30:02

%S 1,2,4,4,6,6,8,8,12,10,12,12,14,14,19,18,18,18,20,20,26,22,26,24,26,

%T 26,36,28,30,32,32,32,40,34,36,36,40,42,50,40,42,42,44,46,54,46,48,48,

%U 55,50,66,52,54,54,60,56,68,60,60,66,62,62,78,64,68,66,68,68,82,70,84,78,74,74,92,76,78

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

%F a(n) = (1/5) * Sum_{d | 5*n-3, d==2 (mod 5)} (d+3).

%F G.f.: Sum_{k>0} x^(2*k-1) / (1 - x^(5*k-4))^2.

%t a[n_] := DivisorSum[5*n - 3, # + 3 &, Mod[#, 5] == 2 &]/5; Array[a, 100] (* _Amiram Eldar_, Jul 06 2023 *)

%o (PARI) a(n) = sumdiv(5*n-3, d, (d%5==2)*(d+3))/5;

%Y Cf. A359237, A363026.

%K nonn

%O 1,2

%A _Seiichi Manyama_, Jul 06 2023