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

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =1a(6) =3a(7) =9a(8) =18a(9) =36a(10) =60a(11) =100a(12) =150a(13) =225a(14) =315a(15) =441a(16) =588a(17) =784a(18) =1008a(19) =1296a(20) =1620a(21) =2025a(22) =2475a(23) =3025a(24) =3630a(25) =4356a(26) =5148a(27) =6084a(28) =7098a(29) =8281