Triangle read by rows: T(n,k) is the number of reverse alternating (i.e., up-down) permutations of {1,2,...,n} having k fixed points (n >= 0, 0 <= k <= 1 + floor(n/2)).
A162980
Triangle read by rows: T(n,k) is the number of reverse alternating (i.e., up-down) permutations of {1,2,...,n} having k fixed points (n >= 0, 0 <= k <= 1 + floor(n/2)).
Terms
- a(0) =1a(1) =0a(2) =1a(3) =0a(4) =0a(5) =1a(6) =1a(7) =1a(8) =2a(9) =2a(10) =1a(11) =6a(12) =6a(13) =3a(14) =1a(15) =22a(16) =22a(17) =12a(18) =4a(19) =1a(20) =102a(21) =102a(22) =51a(23) =15a(24) =2a(25) =506a(26) =506a(27) =264a(28) =88a(29) =19
External references
- oeis: A162980