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 A012709 #10 Nov 21 2013 12:46:01
%S A012709 1,1,3,12,57,340,2305,18186,158977,1560840,16695553,196272142,
%T A012709 2483596577,34036624700,497515462561,7792454528002,129248702613505,
%U A012709 2278494692749840,42291311707716609,828953188249846678
%N A012709 exp(arctanh(x)*exp(x))=1+x+3/2!*x^2+12/3!*x^3+57/4!*x^4+340/5!*x^5...
%F A012709 a(n) ~ (n-1)! * (2*n)^(exp(1)/2) / GAMMA(exp(1)/2). - _Vaclav Kotesovec_, Oct 24 2013
%t A012709 With[{nn=20},CoefficientList[Series[Exp[ArcTanh[x]Exp[x]],{x,0,nn}], x]Range[0,nn]!] (* _Harvey P. Dale_, Jan 14 2012 *)
%K A012709 nonn
%O A012709 0,3
%A A012709 Patrick Demichel (patrick.demichel(AT)hp.com)