This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A261603 #12 Jul 13 2022 21:31:29
%S A261603 1,10,1944,15858432,7763310604800,338060641751949312000,
%T A261603 1761952269949978269865476096000,
%U A261603 1455735772788406631491292993098686136320000,241478064611792629237655079290406479536142910750720000000,10017186663047806334488985920024892176911305625097432121928056832000000000
%N 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.
%F A261603 a(n) = A261602(n, floor(n^2/2)) = A261602(n, ceiling(n^2/2)).
%Y A261603 Main diagonal of A261602.
%K A261603 nonn
%O A261603 1,2
%A A261603 _Max Alekseyev_, Aug 25 2015
%E A261603 a(7)-a(10) from _Max Alekseyev_, Jul 13 2022