a(n) = n*(31*n-1)/2.

Terms

a(0) =0a(1) =15a(2) =61a(3) =138a(4) =246a(5) =385a(6) =555a(7) =756a(8) =988a(9) =1251a(10) =1545a(11) =1870a(12) =2226a(13) =2613a(14) =3031a(15) =3480a(16) =3960a(17) =4471a(18) =5013a(19) =5586a(20) =6190a(21) =6825a(22) =7491a(23) =8188a(24) =8916a(25) =9675a(26) =10465a(27) =11286a(28) =12138a(29) =13021