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

Terms

a(0) =1a(1) =2a(2) =7a(3) =34a(4) =113a(5) =286a(6) =607a(7) =1142a(8) =1969a(9) =3178a(10) =4871a(11) =7162a(12) =10177a(13) =14054a(14) =18943a(15) =25006a(16) =32417a(17) =41362a(18) =52039a(19) =64658a(20) =79441a(21) =96622a(22) =116447a(23) =139174a(24) =165073a(25) =194426a(26) =227527a(27) =264682a(28) =306209a(29) =352438