a(n) = n^3 - n + 1.

Terms

a(0) =1a(1) =1a(2) =7a(3) =25a(4) =61a(5) =121a(6) =211a(7) =337a(8) =505a(9) =721a(10) =991a(11) =1321a(12) =1717a(13) =2185a(14) =2731a(15) =3361a(16) =4081a(17) =4897a(18) =5815a(19) =6841a(20) =7981a(21) =9241a(22) =10627a(23) =12145a(24) =13801a(25) =15601a(26) =17551a(27) =19657a(28) =21925a(29) =24361