a(n) = n^2*(7*n - 5)/2.

Terms

a(0) =0a(1) =1a(2) =18a(3) =72a(4) =184a(5) =375a(6) =666a(7) =1078a(8) =1632a(9) =2349a(10) =3250a(11) =4356a(12) =5688a(13) =7267a(14) =9114a(15) =11250a(16) =13696a(17) =16473a(18) =19602a(19) =23104a(20) =27000a(21) =31311a(22) =36058a(23) =41262a(24) =46944a(25) =53125a(26) =59826a(27) =67068a(28) =74872a(29) =83259