A363359 - OEIS

%I #16 Jul 08 2023 08:04:59

%S 3,7,11,18,19,23,30,31,42,42,43,47,54,66,59,73,67,71,93,79,83,90,98,

%T 114,113,103,107,114,138,126,126,127,131,180,139,154,157,151,186,162,

%U 163,167,193,217,179,186,198,191,252,199,210,233,211,258,222,223,227,252,282,239,273,266,251,324,266,263,270

%N Sum of divisors of 4*n-1 of form 4*k+3.

%F a(n) = A050452(4*n-1).

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

%t a[n_] := DivisorSum[4*n - 1, # &, Mod[#, 4] == 3 &]; Array[a, 100] (* _Amiram Eldar_, Jul 08 2023 *)

%o (PARI) a(n) = sumdiv(4*n-1, d, (d%4==3)*d);

%Y Cf. A050452, A078703, A364085.

%K nonn

%O 1,1

%A _Seiichi Manyama_, Jul 08 2023