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A100686 a(1) = 1, a(2) = 2; thereafter a(2n+1) = |a(2n)^2-a(2n-1)^2|, a(2n+2) = 2*a(2n-1)*a(2n).

%I A100686 #11 Mar 28 2021 09:31:39
%S A100686 1,2,3,4,7,24,527,336,164833,354144,98248054847,116749235904,
%T A100686 3977703802948722503807,22940770664883067253376,
%U A100686 510456831154766758152181998159655209453904127,182503181432559739767250904458105698387204864
%N A100686 a(1) = 1, a(2) = 2; thereafter a(2n+1) = |a(2n)^2-a(2n-1)^2|, a(2n+2) = 2*a(2n-1)*a(2n).
%C A100686 s = 1 and t = 2 are the initial seed numbers; they give the first Pythagorean pair x = 3, y = 4. Then take s = x, t = y for next seed numbers; these give the next Pythagorean pair x = |s^2-t^2|, y = 2st. Then take s = x, t = y and so on.
%H A100686 Planet Math, <a href="https://planetmath.org/pythagoreantriplet">Pythagorean Triplet</a>
%e A100686 a(9) = 527^2-336^2 = 164833 because a(7) = 527 and a(8) = 336.
%K A100686 nonn,easy
%O A100686 1,2
%A A100686 _Pahikkala Jussi_, Dec 08 2004
%E A100686 Edited by _N. J. A. Sloane_, Sep 06 2008
%E A100686 Defined a(2n+1) by absolute values, added 4 values - _R. J. Mathar_, Oct 14 2010