a(n) = (1/6)*(n+1)*(10*n^2 + 17*n + 12).

Terms

a(0) =2a(1) =13a(2) =43a(3) =102a(4) =200a(5) =347a(6) =553a(7) =828a(8) =1182a(9) =1625a(10) =2167a(11) =2818a(12) =3588a(13) =4487a(14) =5525a(15) =6712a(16) =8058a(17) =9573a(18) =11267a(19) =13150a(20) =15232a(21) =17523a(22) =20033a(23) =22772a(24) =25750a(25) =28977a(26) =32463a(27) =36218a(28) =40252a(29) =44575