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 A363647 #13 Jul 17 2023 00:59:13
%S A363647 3,18,91,879,9396,145010,2470665,50728749,1162458352,30058615320,
%T A363647 855935011911,26761537897338,908625319776864,33340089815701086,
%U A363647 1313681976619686558,55341921135416377497,2481720785659010292702,118040125809311823596960
%N A363647 Expansion of Sum_{k>0} (1/(1 - (k*x)^k)^3 - 1).
%F A363647 a(n) = Sum_{d|n} (n/d)^n * binomial(d+2,2).
%t A363647 a[n_] := DivisorSum[n, (n/#)^n * Binomial[# + 2, 2] &]; Array[a, 20] (* _Amiram Eldar_, Jul 17 2023 *)
%o A363647 (PARI) a(n) = sumdiv(n, d, (n/d)^n*binomial(d+2, 2));
%Y A363647 Cf. A023887, A338663, A363646, A363648.
%Y A363647 Cf. A363639.
%K A363647 nonn
%O A363647 1,1
%A A363647 _Seiichi Manyama_, Jun 13 2023