a(n) = n*(2*(n - 2)*n + (-1)^n + 3)/4.

Terms

a(0) =0a(1) =0a(2) =2a(3) =6a(4) =20a(5) =40a(6) =78a(7) =126a(8) =200a(9) =288a(10) =410a(11) =550a(12) =732a(13) =936a(14) =1190a(15) =1470a(16) =1808a(17) =2176a(18) =2610a(19) =3078a(20) =3620a(21) =4200a(22) =4862a(23) =5566a(24) =6360a(25) =7200a(26) =8138a(27) =9126a(28) =10220a(29) =11368