a(n) = n*(7*n^2 - 1)/6.

Terms

a(0) =0a(1) =1a(2) =9a(3) =31a(4) =74a(5) =145a(6) =251a(7) =399a(8) =596a(9) =849a(10) =1165a(11) =1551a(12) =2014a(13) =2561a(14) =3199a(15) =3935a(16) =4776a(17) =5729a(18) =6801a(19) =7999a(20) =9330a(21) =10801a(22) =12419a(23) =14191a(24) =16124a(25) =18225a(26) =20501a(27) =22959a(28) =25606a(29) =28449