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a(n)=number of Gaussian integers z=a+bi satisfying |z|<=n+1/2, a>=0, 0<=b<a.
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%I #10 Jul 14 2019 06:31:11

%S 0,1,3,5,9,13,18,23,29,38,45,54,63,74,85,96,110,124,138,153,167,185,

%T 203,221,239,260,281,301,324,346,371,395,419,445,473,501,530,558,589,

%U 619,652,683,716,751,784,820,855,893,931,970,1010

%N a(n)=number of Gaussian integers z=a+bi satisfying |z|<=n+1/2, a>=0, 0<=b<a.

%H Robert Israel, <a href="/A036713/b036713.txt">Table of n, a(n) for n = 0..2000</a>

%H <a href="/index/Ga#gaussians">Index entries for Gaussian integers and primes</a>

%p N:= 100: V:= Vector(N):

%p for a from 1 to N do

%p for b from 0 to a-1 do

%p nmin:= ceil(sqrt(a^2+b^2)-1/2);

%p if nmin > N then break fi;

%p V[nmin..N]:= V[nmin..N]+~1

%p od od:

%p 0,seq(V[i],i=1..N); # _Robert Israel_, Jul 14 2019

%K nonn

%O 0,3

%A _Clark Kimberling_