Surround numbers of an n X 1 rectangle.

Terms

a(0) =16a(1) =123a(2) =361a(3) =778a(4) =1428a(5) =2371a(6) =3673a(7) =5406a(8) =7648a(9) =10483a(10) =14001a(11) =18298a(12) =23476a(13) =29643a(14) =36913a(15) =45406a(16) =55248a(17) =66571a(18) =79513a(19) =94218a(20) =110836a(21) =129523a(22) =150441a(23) =173758a(24) =199648a(25) =228291a(26) =259873a(27) =294586a(28) =332628a(29) =374203