OFFSET
1,2
COMMENTS
a(n) is the number of nonequivalent binary matrices with 4 distinct columns and any number of nonzero rows with n ones in every column up to permutation of rows and columns.
EXAMPLE
The a(2) = 11 matrices are:
[1 0 0 0] [1 1 0 0] [1 1 1 0] [1 1 0 0] [1 1 0 0]
[1 0 0 0] [1 0 0 0] [1 0 0 0] [1 0 1 0] [1 0 0 0]
[0 1 0 0] [0 1 0 0] [0 1 0 0] [0 1 0 0] [0 1 0 0]
[0 1 0 0] [0 0 1 0] [0 0 1 0] [0 0 1 0] [0 0 1 1]
[0 0 1 0] [0 0 1 0] [0 0 0 1] [0 0 0 1] [0 0 1 0]
[0 0 1 0] [0 0 0 1] [0 0 0 1] [0 0 0 1] [0 0 0 1]
[0 0 0 1] [0 0 0 1]
[0 0 0 1]
.
[1 1 1 1] [1 1 1 0] [1 1 0 0] [1 1 0 0] [1 1 0 1] [1 1 0 0]
[1 0 0 0] [1 0 0 1] [1 0 1 0] [1 0 1 0] [1 0 1 0] [1 0 1 0]
[0 1 0 0] [0 1 0 0] [0 1 1 0] [0 1 0 1] [0 1 1 0] [0 1 0 1]
[0 0 1 0] [0 0 1 0] [0 0 0 1] [0 0 1 0] [0 0 0 1] [0 0 1 1]
[0 0 0 1] [0 0 0 1] [0 0 0 1] [0 0 0 1]
.
A set system corresponding to the first of these is {{1,2}, {3,4}, {5,6}, {7,8}}.
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Andrew Howroyd, Jan 31 2020
STATUS
approved