Number of permutations of {1,...,n} having n-4 inversions (n>=4).

Terms

a(0) =1a(1) =4a(2) =14a(3) =49a(4) =174a(5) =628a(6) =2298a(7) =8504a(8) =31758a(9) =119483a(10) =452284a(11) =1720774a(12) =6574987a(13) =25214332a(14) =96997223a(15) =374153699a(16) =1446677555a(17) =5605337934a(18) =21758936146a(19) =84604366100a(20) =329453055975