n * (11*n^2 + 6*n + 1) / 6.

Terms

a(0) =0a(1) =3a(2) =19a(3) =59a(4) =134a(5) =255a(6) =433a(7) =679a(8) =1004a(9) =1419a(10) =1935a(11) =2563a(12) =3314a(13) =4199a(14) =5229a(15) =6415a(16) =7768a(17) =9299a(18) =11019a(19) =12939a(20) =15070a(21) =17423a(22) =20009a(23) =22839a(24) =25924a(25) =29275a(26) =32903a(27) =36819a(28) =41034a(29) =45559