a(n) = floor(n*(n-1)*(n-2)*(n-3)/5).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =4a(5) =24a(6) =72a(7) =168a(8) =336a(9) =604a(10) =1008a(11) =1584a(12) =2376a(13) =3432a(14) =4804a(15) =6552a(16) =8736a(17) =11424a(18) =14688a(19) =18604a(20) =23256a(21) =28728a(22) =35112a(23) =42504a(24) =51004a(25) =60720a(26) =71760a(27) =84240a(28) =98280a(29) =114004