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 A152189 #18 Apr 12 2014 13:14:39
%S A152189 1,1,1,8,9,55,64,377,441,2584,3025,17711,20736,121393,142129,832040,
%T A152189 974169,5702887,6677056,39088169,45765225,267914296,313679521,
%U A152189 1836311903,2149991424,12586269025,14736260449,86267571272,101003831721,591286729879,692290561600
%N A152189 Product_{k=1..floor((n-1)/2)} (1 + 4*cos(k*Pi/n)^2)*(1 + 4*sin(k*Pi/n)^2).
%C A152189 It appears that limit(sqrt(a(n+2)/a(n)), n->Infinity) = 1+(sqrt(5)+1)/2.
%F A152189 Empirical g.f.: (x^6+x^5-9*x^4+7*x^2-x-1) / ((x-1)*(x+1)*(x^2-3*x+1)*(x^2+3*x+1)). - _Colin Barker_, Apr 11 2014
%t A152189 f[n_] = Product[(1 + 4*Cos[k*Pi/n]^2)*(1 + 4*Sin[k*Pi/n]^2), {k, 1, Floor[(n - 1)/2]}]; Table[N[f[n]], {n, 0, 30}]; Round[%] (* corrected by _Colin Barker_, Apr 11 2014 *)
%o A152189 (PARI) a(n) = round(prod(k=1, floor((n-1)/2), (1+4*cos(k*Pi/n)^2)*(1+4*sin(k*Pi/n)^2))) \\ _Colin Barker_, Apr 11 2014
%Y A152189 Cf. A152191.
%K A152189 nonn
%O A152189 0,4
%A A152189 _Roger L. Bagula_ and _Gary W. Adamson_, Nov 28 2008
%E A152189 Two initial terms added, and several terms corrected by _Colin Barker_, Apr 11 2014