a(n) = n*(1 + n)*(3 - 4*n + 4*n^2)/6.

Terms

a(0) =1a(1) =11a(2) =54a(3) =170a(4) =415a(5) =861a(6) =1596a(7) =2724a(8) =4365a(9) =6655a(10) =9746a(11) =13806a(12) =19019a(13) =25585a(14) =33720a(15) =43656a(16) =55641a(17) =69939a(18) =86830a(19) =106610a(20) =129591a(21) =156101a(22) =186484a(23) =221100a(24) =260325a(25) =304551a(26) =354186a(27) =409654a(28) =471395a(29) =539865