Number of permutations sigma of [n] such that k * sigma(k) >= n for 1 <= k <= n.
A330432
Number of permutations sigma of [n] such that k * sigma(k) >= n for 1 <= k <= n.
Terms
- a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =4a(6) =18a(7) =54a(8) =384a(9) =1920a(10) =15000a(11) =108000a(12) =1270080a(13) =8890560a(14) =126443520a(15) =1440270720a(16) =18811699200a(17) =232243200000
External references
- oeis: A330432