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 A353186 #25 Apr 30 2022 12:19:03 %S A353186 1,1,4,22,170,1588,18236,240840,3662424,62456136,1185150768, %T A353186 24714979584,562659843984,13870798275072,368324715871680, %U A353186 10478253239415552,317975367247809408,10252138622419702656,349999438215928660992,12612365665457524786944,478414908509124826439424 %N A353186 Expansion of e.g.f. 1/(1 - Sum_{k>=1} d(k) * x^k / k), where d(n) = number of divisors of n (A000005). %F A353186 a(0) = 1; a(n) = Sum_{k=1..n} A318249(k) * binomial(n,k) * a(n-k). %t A353186 d[k_] := d[k] = DivisorSigma[0, k]; a[0] = 1; a[n_] := a[n] = Sum[(k - 1)! * d[k] * Binomial[n, k] * a[n - k], {k, 1, n}]; Array[a, 21, 0] (* _Amiram Eldar_, Apr 30 2022 *) %o A353186 (PARI) my(N=30, x='x+O('x^N)); Vec(serlaplace(1/(1-sum(k=1, N, numdiv(k)*x^k/k)))) %o A353186 (PARI) a_vector(n) = my(v=vector(n+1)); v[1]=1; for(i=1, n, v[i+1]=sum(j=1, i, (j-1)!*numdiv(j)*binomial(i, j)*v[i-j+1])); v; %Y A353186 Cf. A000005, A028342, A129921, A305305, A318249, A340903. %K A353186 nonn %O A353186 0,3 %A A353186 _Seiichi Manyama_, Apr 29 2022