a(n) = n*(11*n+1)/2.

Terms

a(0) =0a(1) =6a(2) =23a(3) =51a(4) =90a(5) =140a(6) =201a(7) =273a(8) =356a(9) =450a(10) =555a(11) =671a(12) =798a(13) =936a(14) =1085a(15) =1245a(16) =1416a(17) =1598a(18) =1791a(19) =1995a(20) =2210a(21) =2436a(22) =2673a(23) =2921a(24) =3180a(25) =3450a(26) =3731a(27) =4023a(28) =4326a(29) =4640