Number of permutations p of {1,2,...,n} such that p(i) - i < 0 or p(i) - i > 2 for all i.
A001887
Number of permutations p of {1,2,...,n} such that p(i) - i < 0 or p(i) - i > 2 for all i.
Terms
- a(0) =1a(1) =0a(2) =0a(3) =0a(4) =1a(5) =5a(6) =33a(7) =236a(8) =1918a(9) =17440a(10) =175649a(11) =1942171a(12) =23396353a(13) =305055960a(14) =4280721564a(15) =64330087888
External references
- oeis: A001887