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 A076603 #8 Oct 15 2012 18:41:53
%S A076603 9,40,41,840,841,353640,353641,62530978440,62530978441,
%T A076603 1955061632394403395240,1955061632394403395241,
%U A076603 1911132993230334657643987512400814230724040,1911132993230334657643987512400814230724041
%N A076603 a(1)=9, a(n_even)=(a(n-1)^2-1)/2; a(n_odd)=a(n-1)+1.
%C A076603 {9, 40, 41}, {41, 840, 841}, {841, 353640, 353641}... are sides {a<b<c} of the right triangles, with hypotenuse c=b+1.
%t A076603 nxt[{n_,a_}]:={n+1,If[EvenQ[n+1],(a^2-1)/2,a+1]}; Transpose[ NestList[ nxt,{1,9},10]][[2]] (* _Harvey P. Dale_, Oct 15 2012 *)
%K A076603 easy,nonn
%O A076603 1,1
%A A076603 _Zak Seidov_, Oct 21 2002
%E A076603 More terms from _Harvey P. Dale_, Oct 15 2012