OFFSET
0,3
COMMENTS
The condition that the columns be in nonincreasing order is equivalent to considering nonequivalent matrices up to permutation of columns.
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..200
FORMULA
a(n) = (1/n!)*Sum_{k=0..n} abs(Stirling1(n, k)) * A331644(k).
EXAMPLE
The a(2) = 7 matrices are:
[1 1] [1 0] [1 0] [2 1] [2 0] [1 0] [2 2]
[1 0] [1 1] [0 1] [0 1] [0 2] [1 2]
[0 1] [0 1] [1 1]
CROSSREFS
KEYWORD
nonn
AUTHOR
Andrew Howroyd, Jan 25 2020
STATUS
approved