Number of permutations of {1..n} with n inversions.

Terms

a(0) =1a(1) =0a(2) =0a(3) =1a(4) =5a(5) =22a(6) =90a(7) =359a(8) =1415a(9) =5545a(10) =21670a(11) =84591a(12) =330121a(13) =1288587a(14) =5032235a(15) =19664205a(16) =76893687a(17) =300895513a(18) =1178290263a(19) =4617369760a(20) =18106447251a(21) =71048746505a(22) =278966179936