a(n) = floor(Pi*n^2).

Terms

a(0) =0a(1) =3a(2) =12a(3) =28a(4) =50a(5) =78a(6) =113a(7) =153a(8) =201a(9) =254a(10) =314a(11) =380a(12) =452a(13) =530a(14) =615a(15) =706a(16) =804a(17) =907a(18) =1017a(19) =1134a(20) =1256a(21) =1385a(22) =1520a(23) =1661a(24) =1809a(25) =1963a(26) =2123a(27) =2290a(28) =2463a(29) =2642