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

Terms

a(0) =1a(1) =3a(2) =4a(3) =5a(4) =9a(5) =8a(6) =11a(7) =11a(8) =13a(9) =18a(10) =15a(11) =19a(12) =18a(13) =23a(14) =23a(15) =22a(16) =29a(17) =29a(18) =29a(19) =30a(20) =29a(21) =37a(22) =36a(23) =37a(24) =37a(25) =43a(26) =42a(27) =41a(28) =47a(29) =44