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 A092808 #14 Apr 18 2025 22:22:07
%S A092808 1,0,3,1,11,5,43,21,171,85,683,341,2731,1365,10923,5461,43691,21845,
%T A092808 174763,87381,699051,349525,2796203,1398101,11184811,5592405,44739243,
%U A092808 22369621,178956971,89478485,715827883,357913941,2863311531,1431655765
%N A092808 Pair reversal of Jacobsthal numbers.
%C A092808 a(2n)=A001045(2n+1); a(2n+1)=A001045(2n) a(2n+2)=a(2n)+2*4^n; a(2n+3)=a(2n+1)+4^n.
%H A092808 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (-1,4,4).
%F A092808 G.f.: (1+x-x^2)/((1+x)(1-2x)(1+2x)); E.g.f.: exp(-2x)/4+5exp(2x)/12+exp(-x)/3=cosh(2x)/2+exp(2x)/6+exp(-x)/3; a(n)=(-2)^n/4+5*2^n/12+(-1)^n/3.
%t A092808 LinearRecurrence[{-1,4,4},{1,0,3},40] (* _Harvey P. Dale_, Dec 13 2022 *)
%o A092808 (Python)
%o A092808 def A092808(n): return ((1<<n+(-1 if n&1 else 1))|1)//3 # _Chai Wah Wu_, Apr 18 2025
%K A092808 easy,nonn
%O A092808 0,3
%A A092808 _Paul Barry_, Mar 10 2004