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 A198891 #8 Apr 13 2023 08:29:30
%S A198891 1,1,2,7,32,180,1219,9646,87192,886536,10016159,124481258,1687686528,
%T A198891 24787991800,392081193504,6644677619581,120115898158288,
%U A198891 2307044712629472,46917527736860976,1007152702625923440,22757886107313170356,539955309450787483261,13421068671117864869156
%N A198891 Expansion of e.g.f. 1 / [ Sum_{n>=0} (-x)^(n*(n+1)/2) / (n*(n+1)/2)! ].
%e A198891 E.g.f.: A(x) = 1 + x + 2*x^2/2! + 7*x^3/3! + 32*x^4/4! + 180*x^5/5! + ... + a(n)*x^n/n! + ...
%e A198891 where
%e A198891 1/A(x) = 1 - x - x^3/3! + x^6/6! + x^10/10! - x^15/15! - x^21/21! ++-- ... + (-x)^(n*(n+1)/2)/(n*(n+1)/2)! + ...
%e A198891 1/A(x) = 1 - x - x^3/6 + x^6/720 + x^10/3628800 - x^15/1307674368000 + ...
%o A198891 (PARI) {a(n) = my(A=1/sum(m=0,sqrtint(2*n+1),(-x)^(m*(m+1)/2)/(m*(m+1)/2)!+x*O(x^n))); n!*polcoeff(A,n)}
%o A198891 for(n=0,20, print1(a(n),", "))
%Y A198891 Cf. A198892.
%K A198891 nonn
%O A198891 0,3
%A A198891 _Paul D. Hanna_, Oct 30 2011