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 A191498 #14 May 08 2014 06:37:22
%S A191498 1,1,3,3,-7,25,267,-2261,-9231,284337,-464365,-45533741,430558185,
%T A191498 8212158409,-201645489381,-1064348170245,94082272856033,
%U A191498 -489731454691487,-45404775138028509,840156145287526819,20537314081214613465,-913405900816937424519
%N A191498 E.g.f. sqrt(1+2*x*exp(2*x)).
%F A191498 a(n) = n!*sum(k=1..n, (k^(n-k-1)*(-1)^(k+1)*C(2*k-2,k-1)*2^(n-2*k+1))/(n-k)!), n>0, a(0)=1.
%t A191498 With[{nn=20},CoefficientList[Series[Sqrt[1+2x Exp[2x]],{x,0,nn}], x] Range[0,nn]!] (* _Harvey P. Dale_, Oct 03 2011 *)
%o A191498 (Maxima)
%o A191498 a(n):= n!*sum((k^(n-k-1)*(-1)^(k+1)*binomial(2*k-2,k-1)*2^(n-2*k+1))/(n-k)!, k,1,n);
%K A191498 sign
%O A191498 0,3
%A A191498 _Vladimir Kruchinin_, Jun 03 2011