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

Terms

a(0) =0a(1) =2a(2) =3a(3) =4a(4) =8a(5) =7a(6) =10a(7) =10a(8) =12a(9) =17a(10) =14a(11) =18a(12) =17a(13) =22a(14) =22a(15) =21a(16) =28a(17) =28a(18) =28a(19) =29a(20) =28a(21) =36a(22) =35a(23) =36a(24) =36a(25) =42a(26) =41a(27) =40a(28) =46a(29) =43