a(n) = (4*n^3-3*n^2+5*n-3)/3.

Terms

a(0) =1a(1) =9a(2) =31a(3) =75a(4) =149a(5) =261a(6) =419a(7) =631a(8) =905a(9) =1249a(10) =1671a(11) =2179a(12) =2781a(13) =3485a(14) =4299a(15) =5231a(16) =6289a(17) =7481a(18) =8815a(19) =10299a(20) =11941a(21) =13749a(22) =15731a(23) =17895a(24) =20249a(25) =22801a(26) =25559a(27) =28531a(28) =31725a(29) =35149