A261603 - OEIS

A261603

Number of permutations of the set {1,2,...,n}^2 such that first coordinates of first floor(n^2/2) elements are nondecreasing and second coordinates of the remaining ceiling(n^2/2) elements are nondecreasing.

%I #12 Jul 13 2022 21:31:29

%S 1,10,1944,15858432,7763310604800,338060641751949312000,

%T 1761952269949978269865476096000,

%U 1455735772788406631491292993098686136320000,241478064611792629237655079290406479536142910750720000000,10017186663047806334488985920024892176911305625097432121928056832000000000

%N Number of permutations of the set {1,2,...,n}^2 such that first coordinates of first floor(n^2/2) elements are nondecreasing and second coordinates of the remaining ceiling(n^2/2) elements are nondecreasing.

%F a(n) = A261602(n, floor(n^2/2)) = A261602(n, ceiling(n^2/2)).

%Y Main diagonal of A261602.

%K nonn

%O 1,2

%A _Max Alekseyev_, Aug 25 2015

%E a(7)-a(10) from _Max Alekseyev_, Jul 13 2022