Triangle read by rows: T(n,k) is the number of fixed-point-free involutions of {1,2,...,2n} having k cycles with entries of the same parity (0 <= k <= 2*floor(n/2)).
A161121
Triangle read by rows: T(n,k) is the number of fixed-point-free involutions of {1,2,...,2n} having k cycles with entries of the same parity (0 <= k <= 2*floor(n/2)).
Terms
- a(0) =1a(1) =1a(2) =2a(3) =0a(4) =1a(5) =6a(6) =0a(7) =9a(8) =24a(9) =0a(10) =72a(11) =0a(12) =9a(13) =120a(14) =0a(15) =600a(16) =0a(17) =225a(18) =720a(19) =0a(20) =5400a(21) =0a(22) =4050a(23) =0a(24) =225a(25) =5040a(26) =0a(27) =52920a(28) =0a(29) =66150
External references
- oeis: A161121