a(n) = n*(n + 1)*(11*n^2 + 11*n - 10)/24.

Terms

a(0) =0a(1) =1a(2) =14a(3) =61a(4) =175a(5) =400a(6) =791a(7) =1414a(8) =2346a(9) =3675a(10) =5500a(11) =7931a(12) =11089a(13) =15106a(14) =20125a(15) =26300a(16) =33796a(17) =42789a(18) =53466a(19) =66025a(20) =80675a(21) =97636a(22) =117139a(23) =139426a(24) =164750a(25) =193375a(26) =225576a(27) =261639a(28) =301861a(29) =346550