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 A174562 #20 Dec 23 2023 16:43:01
%S A174562 2,3,5,2,7,5,12,7,19,12,31,19,50,31,81,50,131,81,212,131,343,212,555,
%T A174562 343,898,555,1453,898,2351,1453,3804,2351,6155,3804,9959,6155,16114,
%U A174562 9959,26073,16114,42187,26073,68260,42187,110447,68260,178707,110447
%N A174562 a(1)=2, a(2)=3, then a(n)=a(n-1)+a(n-2) if n odd, a(n)=a(n-1)-a(n-2) if n even.
%H A174562 Harvey P. Dale, <a href="/A174562/b174562.txt">Table of n, a(n) for n = 1..1000</a>
%H A174562 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,1,0,1).
%F A174562 a(n)= a(n-2) +a(n-4). G.f.: x*(-2-3*x-3*x^2+x^3)/(-1+x^2+x^4). a(2n+1) = A001060(n). a(2n) = A013655(n-1). [From _R. J. Mathar_, Apr 14 2010]
%t A174562 nxt[{n_,a_,b_}]:={n+1,b,If[EvenQ[n],b-a,b+a]}; Transpose[ NestList[ nxt,{1,2,3},50]][[2]] (* or *) LinearRecurrence[{0,1,0,1},{2,3,5,2},51] (* _Harvey P. Dale_, Jan 06 2012 *)
%K A174562 nonn,easy
%O A174562 1,1
%A A174562 _Giovanni Teofilatto_, Mar 22 2010
%E A174562 a(44) corrected by _R. J. Mathar_, Apr 14 2010
%E A174562 Precise definition from _R. J. Mathar_, Aug 23 2010