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 A117809 #2 Mar 30 2012 17:34:20
%S A117809 -2,7,3,-26,-13,-7,96,48,24,12,-362,-181,-91,-46,-23,1350,675,337,168,
%T A117809 84,42,-5042,-2521,-1261,-631,-316,-158,-79,18816,9408,4704,2352,1176,
%U A117809 588,294,147,-70226,-35113,-17557,-8779,-4390,-2195,-1098,-549,-275,262086,131043,65521,32760,16380,8190,4095
%N A117809 a(n,m) =Floor[N[(-2 + Sqrt[3])^n + (-2 - Sqrt[3])^n]/2^m].
%C A117809 A triangular prime alternating sign Binet like function.
%e A117809 -2
%e A117809 7, 3
%e A117809 -26, -13,-7
%e A117809 96, 48, 24, 12
%e A117809 -362,-181, -91, -46, -23
%e A117809 1350, 675, 337, 168, 84, 42
%t A117809 f[n_, m_] = N[(-2 + Sqrt[3])^n + (-2 - Sqrt[3])^n]/2^m a = Table[Table[Floor[f[n, m]], {m, 1, n}], {n, 1, 10}] aa = Flatten[a] pp = Flatten[Table[If[PrimeQ[aa[[n]]], aa[[n]], {}], {n, 1, Length[aa]}]] Length[pp]/Length[aa]
%K A117809 sign,tabl
%O A117809 0,1
%A A117809 _Roger L. Bagula_, Apr 29 2006