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 A135753 #13 Nov 06 2016 01:47:18
%S A135753 1,1,3,16,153,2536,72513,3571156,303033153,44411895376,11247688063233,
%T A135753 4933176144494236,3746180187749948193,4933259445571307491096,
%U A135753 11257237602638666745470913,44566655569041016108120599556
%N A135753 E.g.f.: A(x) = Sum_{n>=0} exp((3^n-1)/2*x)*x^n/n!.
%H A135753 G. C. Greubel, <a href="/A135753/b135753.txt">Table of n, a(n) for n = 0..85</a>
%F A135753 a(n) = Sum_{k=0..n} binomial(n,k)*[(3^k-1)/2]^(n-k).
%F A135753 a(n) ~ c * 3^(n^2/4)*2^((n+1)/2)/sqrt(Pi*n), where c = Sum_{k = -infinity..infinity} 2^k*3^(-k^2) = 1.8862156350800186... if n is even and c = Sum_{k = -infinity..infinity} 2^(k+1/2)*3^(-(k+1/2)^2) = 1.8865940733664341... if n is odd. - _Vaclav Kotesovec_, Jun 25 2013
%t A135753 Flatten[{1,Table[Sum[Binomial[n,k]*((3^k-1)/2)^(n-k),{k,0,n}],{n,1,20}]}] (* _Vaclav Kotesovec_, Jun 25 2013 *)
%o A135753 (PARI) a(n)=sum(k=0,n,binomial(n,k)*((3^k-1)/2)^(n-k))
%o A135753 (PARI) a(n)=n!*polcoeff(sum(k=0,n,exp((3^k-1)/2*x)*x^k/k!),n)
%Y A135753 Cf. variants: A001831, A135754.
%K A135753 nonn
%O A135753 0,3
%A A135753 _Paul D. Hanna_, Nov 27 2007