a(n) = (5/6)*n^3+(5/2)*n^2+(8/3)*n.

Terms

a(0) =0a(1) =6a(2) =22a(3) =53a(4) =104a(5) =180a(6) =286a(7) =427a(8) =608a(9) =834a(10) =1110a(11) =1441a(12) =1832a(13) =2288a(14) =2814a(15) =3415a(16) =4096a(17) =4862a(18) =5718a(19) =6669a(20) =7720a(21) =8876a(22) =10142a(23) =11523a(24) =13024a(25) =14650a(26) =16406a(27) =18297a(28) =20328a(29) =22504