Triangle read by rows: T(n,k) is the number of fixed-point-free involutions of {1,2,...,2n} having k descents (n>=1; 1<=k<2n-1).
A161127
Triangle read by rows: T(n,k) is the number of fixed-point-free involutions of {1,2,...,2n} having k descents (n>=1; 1<=k<2n-1).
Terms
- a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =3a(6) =7a(7) =3a(8) =1a(9) =1a(10) =6a(11) =27a(12) =37a(13) =27a(14) =6a(15) =1a(16) =1a(17) =10a(18) =76a(19) =220a(20) =331a(21) =220a(22) =76a(23) =10a(24) =1a(25) =1a(26) =15a(27) =176a(28) =897a(29) =2438
External references
- oeis: A161127