Triangle read by rows: T(n,k) is the number of permutations of {1,2,...,n} such that there are exactly k entries between the entries 1 and 2 (n>=2, 0<=k<=n-2).

A138770

Triangle read by rows: T(n,k) is the number of permutations of {1,2,...,n} such that there are exactly k entries between the entries 1 and 2 (n>=2, 0<=k<=n-2).

Terms

    a(0) =2a(1) =4a(2) =2a(3) =12a(4) =8a(5) =4a(6) =48a(7) =36a(8) =24a(9) =12a(10) =240a(11) =192a(12) =144a(13) =96a(14) =48a(15) =1440a(16) =1200a(17) =960a(18) =720a(19) =480a(20) =240a(21) =10080a(22) =8640a(23) =7200a(24) =5760a(25) =4320a(26) =2880a(27) =1440a(28) =80640a(29) =70560

External references