a(n) = floor(n/2) * floor((n-1)/2) * floor((n-2)/2) * floor((n-3)/2) * floor((n-4)/2) / 12.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =1a(7) =3a(8) =12a(9) =24a(10) =60a(11) =100a(12) =200a(13) =300a(14) =525a(15) =735a(16) =1176a(17) =1568a(18) =2352a(19) =3024a(20) =4320a(21) =5400a(22) =7425a(23) =9075a(24) =12100a(25) =14520a(26) =18876a(27) =22308a(28) =28392a(29) =33124