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

Terms

a(0) =1a(1) =3a(2) =5a(3) =8a(4) =13a(5) =17a(6) =23a(7) =29a(8) =36a(9) =45a(10) =53a(11) =63a(12) =72a(13) =84a(14) =96a(15) =107a(16) =122a(17) =137a(18) =152a(19) =167a(20) =182a(21) =201a(22) =219a(23) =238a(24) =257a(25) =279a(26) =300a(27) =321a(28) =345a(29) =367