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 A189238 #14 Jun 02 2025 04:01:30
%S A189238 1,2,6,28,120,726,4424,31928,249984,2131690,20027392,199240020,
%T A189238 2162269824,24676708798,302660939520,3897794538864,53264941301760,
%U A189238 763279034957010,11499327153704960,181271619624350860
%N A189238 E.g.f. x/cos(x)*exp(x/cos(x)).
%C A189238 A(x)=A009843(x)*exp(A009843(x)).
%H A189238 Vincenzo Librandi, <a href="/A189238/b189238.txt">Table of n, a(n) for n = 1..100</a>
%F A189238 a(n)=sum(k=1..n-1, binomial(n,k)*k*(1+(-1)^(n-k))*sum(j=1..m, sum(i=0..floor((j-1)/2), binomial(m,j)/2^(j)*sum((-1)^((n-k)/2-j)*binomial(j,i)*(j-2*i)^(n-k)))*binomial(k+m-1,k-1),m,1,n-k))+n.
%o A189238 (Maxima)
%o A189238 a(n):=sum(binomial(n,k)*k*(1+(-1)^(n-k))*sum(sum(binomial(m,j)/2^(j)*sum((-1)^((n-k)/2-j)*binomial(j,i)*(j-2*i)^(n-k),i,0,floor((j-1)/2)),j,1,m)*binomial(k+m-1,k-1),m,1,n-k),k,1,n-1)+n;
%o A189238 (PARI) x='x+O('x^66); /* that many terms */
%o A189238 egf=x/cos(x)*exp(x/cos(x)); /* = x + x^2 + x^3 + 7/6*x^4 + x^5 + 121/120*x^6+ ... */
%o A189238 Vec(serlaplace(egf)) /* show terms */ /* Joerg Arndt, Apr 21 2011 */
%K A189238 nonn
%O A189238 1,2
%A A189238 _Vladimir Kruchinin_, Apr 19 2011