(8*n^3 + 3*n^2 + n) / 6.

Terms

a(0) =2a(1) =13a(2) =41a(3) =94a(4) =180a(5) =307a(6) =483a(7) =716a(8) =1014a(9) =1385a(10) =1837a(11) =2378a(12) =3016a(13) =3759a(14) =4615a(15) =5592a(16) =6698a(17) =7941a(18) =9329a(19) =10870a(20) =12572a(21) =14443a(22) =16491a(23) =18724a(24) =21150a(25) =23777a(26) =26613a(27) =29666a(28) =32944a(29) =36455