Number of 2 up, 2 down, 2 up, ... permutations of length 2n + 1.
A005981
Number of 2 up, 2 down, 2 up, ... permutations of length 2n + 1.
Terms
- a(0) =1a(1) =1a(2) =6a(3) =71a(4) =1456a(5) =45541a(6) =2020656a(7) =120686411a(8) =9336345856a(9) =908138776681
External references
- oeis: A005981