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 A028894 #11 Jul 03 2025 18:23:18
%S A028894 1,5,23,95,381,1527,6109,24439,97759,391037,1564151,6256607,25026429,
%T A028894 100105719,400422877,1601691511,6406766047,25627064189,102508256759,
%U A028894 410033027037,1640132108151,6560528432607,26242113730429
%N A028894 a(n) = either 4a(n-1)+1 or 4a(n-1)+3 depending on corresponding term of A005614, +1 for 0, +3 for 1.
%t A028894 f[1]={0}; f[2]={1}; f[n_] := f[n]=Join[f[n-1], f[n-2]]; a[1]=1; a[n_] := a[n]=4a[n-1]+1+2f[9][[n]]; a/@Range[1, 30]
%Y A028894 Related to A005614, A002450, A037576, A066744.
%K A028894 nonn
%O A028894 1,2
%A A028894 _John McNamara_, Jan 12 2002
%E A028894 Edited by _Dean Hickerson_, Jan 14 2002