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%I #12 Aug 14 2023 02:00:29
%S 1,5,37,517,10001,248873,7529537,268435973,11019960613,512000010005,
%T 26559922791425,1521681143418409,95428956661682177,
%U 6502111422505477189,478296900000000010037,37778931862957430145541,3189059870763703892770817
%N a(n) = Sum_{d|n} (2*d)^(d-1).
%F G.f.: Sum_{k>0} (2 * k)^(k-1) * x^k / (1 - x^k).
%t a[n_] := DivisorSum[n, (2*#)^(# - 1) &]; Array[a, 20] (* _Amiram Eldar_, Aug 14 2023 *)
%o (PARI) a(n) = sumdiv(n, d, (2*d)^(d-1));
%o (PARI) my(N=20, x='x+O('x^N)); Vec(sum(k=1, N, (2*k)^(k-1)*x^k/(1-x^k)))
%Y Cf. A262843, A359731.
%K nonn,easy
%O 1,2
%A _Seiichi Manyama_, Jan 13 2023
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