Number of permutations of (1,...,n) having n-3 inversions (n>=3).

Terms

a(0) =1a(1) =3a(2) =9a(3) =29a(4) =98a(5) =343a(6) =1230a(7) =4489a(8) =16599a(9) =61997a(10) =233389a(11) =884170a(12) =3366951a(13) =12876702a(14) =49424984a(15) =190297064a(16) =734644291a(17) =2842707951a(18) =11022366544a(19) =42815701060a(20) =166583279325a(21) =649063995030