A359796 a(n) = Sum_{d|n} (2*d)^(d-1).
1, 5, 37, 517, 10001, 248873, 7529537, 268435973, 11019960613, 512000010005, 26559922791425, 1521681143418409, 95428956661682177, 6502111422505477189, 478296900000000010037, 37778931862957430145541, 3189059870763703892770817
Offset: 1
Programs
-
Mathematica
a[n_] := DivisorSum[n, (2*#)^(# - 1) &]; Array[a, 20] (* Amiram Eldar, Aug 14 2023 *)
-
PARI
a(n) = sumdiv(n, d, (2*d)^(d-1));
-
PARI
my(N=20, x='x+O('x^N)); Vec(sum(k=1, N, (2*k)^(k-1)*x^k/(1-x^k)))
Formula
G.f.: Sum_{k>0} (2 * k)^(k-1) * x^k / (1 - x^k).