Triangle read by rows: T(n,k) is the number of permutations of {1,2,...,n} whose 2nd cycle has k entries; each cycle is written with the smallest element first and cycles are arranged in increasing order of their first elements (n>=1; 0<=k<=n-1). For example, 1432=(1)(24)(3) has 2 entries in the 2nd cycle; 3421=(1324) has 0 entries in the 2nd cycle.
A138771
Triangle read by rows: T(n,k) is the number of permutations of {1,2,...,n} whose 2nd cycle has k entries; each cycle is written with the smallest element first and cycles are arranged in increasing order of their first elements (n>=1; 0<=k<=n-1). For example, 1432=(1)(24)(3) has 2 entries in the 2nd cycle; 3421=(1324) has 0 entries in the 2nd cycle.
Terms
- a(0) =1a(1) =1a(2) =1a(3) =2a(4) =3a(5) =1a(6) =6a(7) =11a(8) =5a(9) =2a(10) =24a(11) =50a(12) =26a(13) =14a(14) =6a(15) =120a(16) =274a(17) =154a(18) =94a(19) =54a(20) =24a(21) =720a(22) =1764a(23) =1044a(24) =684a(25) =444a(26) =264a(27) =120a(28) =5040a(29) =13068
External references
- oeis: A138771