Number of paths through an array.

Terms

a(0) =0a(1) =0a(2) =2a(3) =15a(4) =104a(5) =770a(6) =6264a(7) =56196a(8) =554112a(9) =5973264a(10) =69998400a(11) =886897440a(12) =12089295360a(13) =176484597120