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 A135754 #10 Nov 07 2016 11:26:43
%S A135754 1,1,3,19,239,6091,305023,30818299,6155906879,2484667187371,
%T A135754 1989929726352863,3221489148102557179,10362312712649347408159,
%U A135754 67345216546226371822133611,869978904614825017953532433663
%N A135754 E.g.f.: A(x) = Sum_{n>=0} exp((4^n-1)/3*x)*x^n/n!.
%H A135754 G. C. Greubel, <a href="/A135754/b135754.txt">Table of n, a(n) for n = 0..80</a>
%F A135754 a(n) = Sum_{k=0..n} C(n,k)*[(4^k-1)/3]^(n-k).
%F A135754 a(n) ~ c * 2^(n^2/2+n+1/2)/(3^(n/2)*sqrt(Pi*n)), where c = Sum_{k = -infinity..infinity} 3^k*4^(-k^2) = 1.86902676808473931... if n is even and c = Sum_{k = -infinity..infinity} 3^(k+1/2)*4^(-(k+1/2)^2) = 1.87384213421283135... if n is odd. - _Vaclav Kotesovec_, Jun 25 2013
%t A135754 Flatten[{1,Table[Sum[Binomial[n,k]*((4^k-1)/3)^(n-k),{k,0,n}],{n,1,20}]}] (* _Vaclav Kotesovec_, Jun 25 2013 *)
%o A135754 (PARI) a(n)=sum(k=0,n,binomial(n,k)*((4^k-1)/3)^(n-k))
%o A135754 (PARI) a(n)=n!*polcoeff(sum(k=0,n,exp((4^k-1)/3*x)*x^k/k!),n)
%Y A135754 Cf. variants: A001831, A135753.
%K A135754 nonn
%O A135754 0,3
%A A135754 _Paul D. Hanna_, Nov 27 2007