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 A117271 #7 May 09 2014 18:24:15
%S A117271 0,1,2,12,134,2100,42302,1041852,30331814,1019056260,38805685262,
%T A117271 1651676734092,77703508288694,4003868870257620,224255353667365022,
%U A117271 13565588100060643932,881405810330856632774,61218510507062012550180
%N A117271 Column 0 of triangle A117270, which is the matrix log of triangle A117269.
%F A117271 E.g.f.: A(x) = log( (3-sqrt(5-4*exp(x)))/2 ).
%F A117271 a(n) ~ sqrt(10) * n^(n-1) / (6 * exp(n) * (log(5)-2*log(2))^(n-1/2)). - _Vaclav Kotesovec_, Feb 25 2014
%o A117271 (PARI) {a(n)=local(C=matrix(n+1,n+1,r,c,if(r>=c,binomial(r-1,c-1))),M=C,L); for(i=1,n+1,M=(M-M^0)^2+C);L=sum(r=1,#M,-(M^0-M)^r/r);return(L[n+1,1])}
%Y A117271 Cf. A117269, A117270.
%K A117271 nonn
%O A117271 0,3
%A A117271 _Paul D. Hanna_, Mar 05 2006