a(n)=number of numbers h^2+k^2 that are <=2n^2; equivalently, a(n)=T(n,n), array T as in A048149.

Terms

a(0) =1a(1) =4a(2) =9a(3) =20a(4) =31a(5) =48a(6) =65a(7) =86a(8) =113a(9) =140a(10) =173a(11) =206a(12) =239a(13) =286a(14) =327a(15) =378a(16) =425a(17) =478a(18) =533a(19) =590a(20) =659a(21) =722a(22) =793a(23) =862a(24) =933a(25) =1020a(26) =1099a(27) =1184a(28) =1271a(29) =1360