Number of permutations of 3 indistinguishable copies of 1,...,n such that the first and second copies of j are adjacent and there are exactly j-1 numbers between the second and the third copy of j.
A321956
Number of permutations of 3 indistinguishable copies of 1,...,n such that the first and second copies of j are adjacent and there are exactly j-1 numbers between the second and the third copy of j.
Terms
- a(0) =1a(1) =1a(2) =0a(3) =2a(4) =4a(5) =0a(6) =16a(7) =40a(8) =0a(9) =456a(10) =1759a(11) =0a(12) =34636a(13) =175198a(14) =0a(15) =5494621a(16) =34043062a(17) =0a(18) =1566676831a(19) =11595162169a(20) =0a(21) =733941313543a(23) =0
External references
- oeis: A321956