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a(1) = 11, a(n_even) = (a(n-1)^2-1)/2; a(n_odd) = a(n-1)+1.
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%I #8 Apr 17 2022 20:12:59

%S 11,60,61,1860,1861,1731660,1731661,1499324909460,1499324909461,

%T 1123987592065117923655260,1123987592065117923655261,

%U 631674053558170970207436821512098200057586489060

%N a(1) = 11, a(n_even) = (a(n-1)^2-1)/2; a(n_odd) = a(n-1)+1.

%C {11, 60, 61}, {61, 1860, 1861}, {1861, 1731660, 1731661}... are sides {a<b<c} of the right triangles, with hypotenuse c = b+1.

%K easy,nonn

%O 1,1

%A _Zak Seidov_, Oct 21 2002

%E a(12) from _Lars Blomberg_, Oct 08 2008