C(2*n+4,4)-C(2*n,4).

Terms

a(0) =1a(1) =15a(2) =69a(3) =195a(4) =425a(5) =791a(6) =1325a(7) =2059a(8) =3025a(9) =4255a(10) =5781a(11) =7635a(12) =9849a(13) =12455a(14) =15485a(15) =18971a(16) =22945a(17) =27439a(18) =32485a(19) =38115a(20) =44361a(21) =51255a(22) =58829a(23) =67115a(24) =76145a(25) =85951a(26) =96565a(27) =108019a(28) =120345a(29) =133575