Number of permutations of (1,...,n) having n-5 inversions (n>=5).

Terms

a(0) =1a(1) =5a(2) =20a(3) =76a(4) =285a(5) =1068a(6) =4015a(7) =15159a(8) =57486a(9) =218895a(10) =836604a(11) =3208036a(12) =12337630a(13) =47572239a(14) =183856635a(15) =712033264a(16) =2762629983a(17) =10736569602a(18) =41788665040a(19) =162869776650a(20) =635562468075