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 A004040 #13 Oct 24 2023 07:10:46
%S A004040 1,2,6,23,103,512,2740,15485,91245,555662,3475090,22214707,144640291,
%T A004040 956560748,6411521056,43478151737,297864793993,2059159989914,
%U A004040 14350039389022,100726680316559,711630547589023,5057282786190872,36132861123763276,259423620328055093,1870954187618001253
%N A004040 Inversion of A000257.
%F A004040 Invert: define b by 1+Sum a(n)x^n = 1/(1 - Sum b(n)x^n).
%o A004040 (PARI) x='x+O('x^66); Vec( -1 + 32*x/(1+20*x-8*x^2-(1-8*x)^(3/2)) ) \\ _Joerg Arndt_, May 04 2013
%Y A004040 Cf. A000257.
%Y A004040 Essentially the same as A022558.
%K A004040 nonn
%O A004040 0,2
%A A004040 _N. J. A. Sloane_
%E A004040 More terms from _Joerg Arndt_, May 04 2013