a(n) = (mu(n)+2)*n^2, where mu is the Moebius function (A008683).

Terms

a(0) =3a(1) =4a(2) =9a(3) =32a(4) =25a(5) =108a(6) =49a(7) =128a(8) =162a(9) =300a(10) =121a(11) =288a(12) =169a(13) =588a(14) =675a(15) =512a(16) =289a(17) =648a(18) =361a(19) =800a(20) =1323a(21) =1452a(22) =529a(23) =1152a(24) =1250a(25) =2028a(26) =1458a(27) =1568a(28) =841a(29) =900