a(n) = (122n^3 + 140n^2 + 45n + 3n(-1)^n)/8.

Terms

a(0) =0a(1) =38a(2) =204a(3) =585a(4) =1280a(5) =2370a(6) =3960a(7) =6125a(8) =8976a(9) =12582a(10) =17060a(11) =22473a(12) =28944a(13) =36530a(14) =45360a(15) =55485a(16) =67040a(17) =80070a(18) =94716a(19) =111017a(20) =129120a(21) =149058a(22) =170984a(23) =194925a(24) =221040a(25) =249350