This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A360797 #15 Jul 31 2023 02:25:08 %S A360797 1,5,13,39,81,225,449,1115,2345,5373,11265,25483,53249,116497,246405, %T A360797 529195,1114113,2372741,4980737,10515511,22025617,46204953,96468993, %U A360797 201506607,419432417,872787997,1811981789,3758970975,7784628225,16108217801,33285996545,68723976779 %N A360797 Expansion of Sum_{k>0} x^k / (1 - 2 * x^k)^(k+1). %F A360797 a(n) = Sum_{d|n} 2^(n/d-1) * binomial(d+n/d-1,d). %F A360797 If p is prime, a(p) = 1 + p * 2^(p-1). %t A360797 a[n_] := DivisorSum[n, 2^(n/# - 1) * Binomial[# + n/# - 1, #] &]; Array[a, 30] (* _Amiram Eldar_, Jul 31 2023 *) %o A360797 (PARI) my(N=40, x='x+O('x^N)); Vec(sum(k=1, N, x^k/(1-2*x^k)^(k+1))) %o A360797 (PARI) a(n) = sumdiv(n, d, 2^(n/d-1)*binomial(d+n/d-1, d)); %Y A360797 Cf. A360798. %K A360797 nonn %O A360797 1,2 %A A360797 _Seiichi Manyama_, Feb 21 2023