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 A186271 #8 Jul 11 2015 08:21:59
%S A186271 1,1,3,21,357,14637,1449063,346326057,199830134889,278363377900377,
%T A186271 936136039878967851,7600488507777339982269,
%U A186271 148977175240943640992454669,7049748909576694035403947391749,805384464676770256686653161875581007
%N A186271 a(n)=Product{k=0..n, A001333(k)}.
%C A186271 a(n) is the determinant of the symmetric matrix (if(j<=floor((i+j)/2), Pell(j+1),
%C A186271 Pell(i+1)))_{0<=i,j<=n}, where Pell(n)=A000129(n).
%F A186271 a(n)=Product{k=0..n, sum{j=0..floor(k/2), binomial(k,2j)*2^j}}.
%F A186271 a(n) ~ c * (1+sqrt(2))^(n*(n+1)/2) / 2^(n+1), where c = 1.6982679851338713863950411843311686297311132648098280324748781109134... . - _Vaclav Kotesovec_, Jul 11 2015
%e A186271 a(3)=21 since det[1, 1, 1, 1; 1, 2, 2, 2; 1, 2, 5, 5; 1, 2, 5, 12]=21.
%t A186271 Table[Product[Sum[Binomial[k,2*j]*2^j,{j,0,Floor[k/2]}],{k,0,n}],{n,0,15}] (* _Vaclav Kotesovec_, Jul 11 2015 *)
%t A186271 Table[FullSimplify[Product[((1+Sqrt[2])^k + (1-Sqrt[2])^k)/2, {k, 0, n}]], {n, 0, 15}] (* _Vaclav Kotesovec_, Jul 11 2015 *)
%Y A186271 Cf. A186269.
%K A186271 nonn,easy
%O A186271 0,3
%A A186271 _Paul Barry_, Feb 16 2011