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 A373275 #10 May 29 2024 13:48:57
%S A373275 1,1,5,5,17,29,65,117,261,497,1025,2017,4097,8129,16405,32629,65537,
%T A373275 130845,262145,523765,1048645,2096129,4194305,8386641,16777233,
%U A373275 33550337,67109125,134209477,268435457,536855053,1073741825,2147450741,4294968325,8589869057
%N A373275 a(n) = Sum_{d|n} (-1)^(d-1) * 2^(n/d-1).
%F A373275 G.f.: 1/2 * Sum_{k>=1} (2*x)^k / (1 + x^k).
%F A373275 If p is an odd prime, a(p) = 1 + 2^(p-1).
%o A373275 (PARI) a(n) = sumdiv(n, d, (-1)^(d-1)*2^(n/d-1));
%o A373275 (PARI) my(N=40, x='x+O('x^N)); Vec(sum(k=1, N, (2*x)^k/(1+x^k))/2)
%Y A373275 Cf. A048272, A373276.
%Y A373275 Cf. A034729, A321386.
%K A373275 nonn,easy
%O A373275 1,3
%A A373275 _Seiichi Manyama_, May 29 2024