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.
{a(n)=local(X=x+x*O(x^n), Egf); Egf=sum(m=0, n, x^m*prod(k=1, m, cosh(k*X))); if(n<1,0,(n-1)!*polcoeff(Egf, n))}
E.g.f.: A(x) = 1 + x + 4*x^2/2! + 27*x^3/3! + 280*x^4/4! + 4025*x^5/5! + 75876*x^6/6! + 1800253*x^7/7! +... where A(x) = 1 + x*exp(x) + x^2*exp(3*x) + x^3*exp(6*x) + x^4*exp(10*x) +... By a q-series identity: A(x) = 1 + x*exp(x)*(1-x*exp(x))/(1-x*exp(2*x)) + x^2*exp(2*x)*(1-x*exp(x))*(1-x*exp(3*x))/((1-x*exp(2*x))*(1-x*exp(4*x))) + x^3*exp(3*x)*(1-x*exp(x))*(1-x*exp(3*x))*(1-x*exp(5*x))/((1-x*exp(2*x))*(1-x*exp(4*x))*(1-x*exp(6*x))) +...
{a(n)=local(Egf); Egf=sum(m=0, n, x^m*exp(m*(m+1)/2*x+x*O(x^n))); n!*polcoeff(Egf, n)}
/* q-series identity: */
{a(n)=local(A=1+x);for(i=1, n, A=sum(m=0, n, x^m*exp(m*x+x*O(x^n))*prod(k=1, m, (1-x*exp((2*k-1)*x+x*O(x^n)))/(1-x*exp((2*k)*x+x*O(x^n)))))); n!*polcoeff(A, n)}
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