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Smallest a(n)>a(n-1) such that a(n)^2+a(n-1)^2 is a perfect square, a(1)=9.
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%I #8 May 01 2014 10:38:53

%S 9,12,16,30,40,42,56,90,120,126,168,224,360,378,504,550,1320,1386,

%T 1848,1989,2652,2961,3948,5264,8052,9711,12948,17264,24852,31311,

%U 41748,53289,71052,94736,130548,145061,146280,153594,163392,170280,173290

%N Smallest a(n)>a(n-1) such that a(n)^2+a(n-1)^2 is a perfect square, a(1)=9.

%C The sequence is infinite.

%F a(n)=A076671(n), n>1. [From _R. J. Mathar_, Sep 20 2008]

%t ps[n_]:=Module[{k=n+1,n2=n^2},While[!IntegerQ[Sqrt[n2+k^2]],k++];k]; NestList[ ps,9,40] (* _Harvey P. Dale_, May 01 2014 *)

%Y Cf. A076600.

%K nonn

%O 1,1

%A _Zak Seidov_, Oct 25 2002