Triangle read by rows: T(n,k) is the number of derangements of {1,2,...,n} having k cycles of length 2 (0 <= k <= floor(n/2)).

A162974

Triangle read by rows: T(n,k) is the number of derangements of {1,2,...,n} having k cycles of length 2 (0 <= k <= floor(n/2)).

Terms

    a(0) =1a(1) =0a(2) =0a(3) =1a(4) =2a(5) =0a(6) =6a(7) =0a(8) =3a(9) =24a(10) =20a(11) =0a(12) =160a(13) =90a(14) =0a(15) =15a(16) =1140a(17) =504a(18) =210a(19) =0a(20) =8988a(21) =4480a(22) =1260a(23) =0a(24) =105a(25) =80864a(26) =41040a(27) =9072a(28) =2520a(29) =0

External references