A363291 - OEIS

%I #14 Jul 08 2023 08:05:10

%S 1,1,1,6,1,1,10,1,6,14,1,1,18,6,1,31,1,1,31,1,1,30,14,6,43,1,1,38,6,

%T 18,42,1,1,60,1,14,71,1,6,54,1,1,67,31,1,62,18,1,84,1,30,79,1,6,74,1,

%U 1,132,6,1,91,14,1,108,38,1,90,1,31,103,1,42,98,6,14,102,1,1,186,30,18,110,1,6,114,50,1

%N Sum of divisors of 4*n-1 of form 4*k+1.

%F a(n) = A050449(4*n-1).

%F G.f.: Sum_{k>0} (4*k-3) * x^(3*k-2) / (1 - x^(4*k-3)).

%t a[n_] := DivisorSum[4*n - 1, # &, Mod[#, 4] == 1 &]; Array[a, 100] (* _Amiram Eldar_, Jul 08 2023 *)

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

%Y Cf. A050449, A078703, A364082.

%K nonn

%O 1,4

%A _Seiichi Manyama_, Jul 08 2023