OFFSET
0,3
COMMENTS
Also, the number of n X 4 {-1,0,1} matrices with all rows and columns summing to zero up to permutations of rows.
EXAMPLE
The a(2) = 10 matrices are:
[1 1 2 0] [1 2 1 0] [1 2 0 1] [2 1 1 0] [2 1 0 1] [2 0 1 1]
[1 1 0 2] [1 0 1 2] [1 0 2 1] [0 1 1 2] [0 1 2 1] [0 2 1 1]
.
[1 1 1 1] [2 2 0 0] [2 0 2 0] [2 0 0 2]
[1 1 1 1] [0 0 2 2] [0 2 0 2] [0 2 2 0]
CROSSREFS
KEYWORD
nonn
AUTHOR
Andrew Howroyd, Oct 15 2024
STATUS
approved