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%I #12 May 08 2022 08:47:58
%S 0,1,1,1,2,2,2,2,2,3,3,3,4,4,4,4,5,5,5,5,5,5,5,5,6,7,7,7,8,8,8,8,8,9,
%T 9,9,10,10,10,10,11,11,11,11,11,11,11,11,11,12,12,12,13,13,13,13,13,
%U 14,14,14,15,15,15,15,16,16,16,16,16,16,16,16,17,18,18,18,18,18,18,18,18,19
%N Number of positive integers <= n that can be expressed as a sum of 2 coprime squares > 0.
%D Steven R. Finch, Mathematical Constants, Cambridge, 2003, p. 100
%H Amiram Eldar, <a href="/A090736/b090736.txt">Table of n, a(n) for n = 1..10000</a>
%F a(n) is asymptotic to (3/(8*K))*n/sqrt(log(n)) where K is the Landau-Ramanujan constant (A064533).
%t Accumulate[Table[Boole[n > 1 && IntegerExponent[n, 2] < 2 && AllTrue[FactorInteger[n][[;; , 1]], Mod[#, 4] < 3 &]], {n, 1, 100}]] (* _Amiram Eldar_, May 08 2022 *)
%o (PARI) a(n)=sum(i=1,n,if(sum(u=1,i,sum(v=1,u,if(abs(u^2+v^2-i)+abs(gcd(u,v)-1),0,1))),1,0))
%Y Cf. A008784, A064533, A090735.
%K nonn
%O 1,5
%A _Benoit Cloitre_, Jan 18 2004
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