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%I #16 Dec 09 2014 03:34:34
%S 0,0,1,0,1,2,0,1,2,0,1,3,2,0,1,2,4,3,0,1,2,4,3,0,1,4,2,3,5,0,1,2,6,3,
%T 5,4,0,1,2,5,3,4,7,0,1,2,5,3,7,4,6,0,1,2,8,3,6,4,0,1,5,2,7,3,6,4,9,8,
%U 0,1,2,3,6,9,4,7,5,0,1,2,9,3,8,4,7,5,0
%N Smallest k such that k^2 + l^2 = n-th number expressible as sum of two squares (A001481).
%C a(n) = 0 if A001481(n) is square. Conjecture: the values between two zeros are always distinct from each other.
%e The 6th number expressible as sum of two squares A001481(6) = 8 = 2^2 + 2^2, so a(6)=2.
%o (PARI) for(n=1, 300,s=sqrtint(n);forstep(i=s,1,-1,if(issquare(n-i*i),print1(sqrtint(n-i*i), ",");break)))
%K nonn
%O 1,6
%A _Ralf Stephan_, Sep 15 2013
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