Number of ways to place 2n rooks on an n X n board, with 2 rooks in each row and each column, multiple rooks in a cell allowed, and exactly 2 rooks below the main diagonal.
A260585
Number of ways to place 2n rooks on an n X n board, with 2 rooks in each row and each column, multiple rooks in a cell allowed, and exactly 2 rooks below the main diagonal.
Terms
- a(0) =1a(1) =11a(2) =72a(3) =367a(4) =1630a(5) =6680a(6) =26082a(7) =98870a(8) =368045a(9) =1354850a(10) =4953503a(11) =18035279a(12) =65499031a(13) =237511321a(14) =860471110a(15) =3115667369a(16) =11277816388a(17) =40814611818a(18) =147692103728a(19) =534404499040
External references
- oeis: A260585