a(n) = n*(n^3 + 2*n^2 - 5*n + 10)/8.

Terms

a(0) =0a(1) =1a(2) =4a(3) =15a(4) =43a(5) =100a(6) =201a(7) =364a(8) =610a(9) =963a(10) =1450a(11) =2101a(12) =2949a(13) =4030a(14) =5383a(15) =7050a(16) =9076a(17) =11509a(18) =14400a(19) =17803a(20) =21775a(21) =26376a(22) =31669a(23) =37720a(24) =44598a(25) =52375a(26) =61126a(27) =70929a(28) =81865a(29) =94018