Triangle read by rows: T(n,k) is the number of permutations of {1,2,...,n} having k nonincreasing even cycles (0<=k<=floor(n/4)). A cycle (b(1), b(2), ...) is said to be increasing if, when written with its smallest element in the first position, it satisfies b(1)<b(2)<b(3)<... . A cycle is said to be even if it has an even number of entries. For example, the permutation (1528)(347)(6) has 1 nonincreasing even cycles.
A186769
Triangle read by rows: T(n,k) is the number of permutations of {1,2,...,n} having k nonincreasing even cycles (0<=k<=floor(n/4)). A cycle (b(1), b(2), ...) is said to be increasing if, when written with its smallest element in the first position, it satisfies b(1)<b(2)<b(3)<... . A cycle is said to be even if it has an even number of entries. For example, the permutation (1528)(347)(6) has 1 nonincreasing even cycles.
Terms
- a(0) =1a(1) =1a(2) =2a(3) =6a(4) =19a(5) =5a(6) =95a(7) =25a(8) =451a(9) =269a(10) =3157a(11) =1883a(12) =21092a(13) =18353a(14) =875a(15) =189828a(16) =165177a(17) =7875a(18) =1660351a(19) =1764749a(20) =203700a(21) =18263861a(22) =19412239a(23) =2240700a(24) =197541565a(25) =237001478a(26) =43736682a(27) =721875a(28) =2568040345a(29) =3081019214
External references
- oeis: A186769