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

Terms

a(0) =1a(1) =8a(2) =26a(3) =61a(4) =119a(5) =206a(6) =328a(7) =491a(8) =701a(9) =964a(10) =1286a(11) =1673a(12) =2131a(13) =2666a(14) =3284a(15) =3991a(16) =4793a(17) =5696a(18) =6706a(19) =7829a(20) =9071a(21) =10438a(22) =11936a(23) =13571a(24) =15349a(25) =17276a(26) =19358a(27) =21601a(28) =24011a(29) =26594