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

Terms

a(0) =1a(1) =3a(2) =5a(3) =9a(4) =11a(5) =17a(6) =17a(7) =19a(8) =25a(9) =29a(10) =33a(11) =31a(12) =33a(13) =45a(14) =43a(15) =49a(16) =45a(17) =53a(18) =55a(19) =61a(20) =65a(21) =59a(22) =73a(23) =69a(24) =71a(25) =85a(26) =81a(27) =85a(28) =83a(29) =89