OFFSET
4,2
COMMENTS
From R. J. Mathar, Apr 07 2017: (Start)
These are the row sums of the following triangle, which shows in row n and column t the number of symmetric n X n {0,1}-matrices with trace t and 4 ones in each row and each column, 0 <= t <= n:
0: 1;
1: 0, 0;
2: 0, 0, 0;
3: 0, 0, 0, 0;
4: 0, 0, 0, 0, 1;
5: 1, 0, 10, 0, 15, 0;
6: 15, 0, 270, 0, 465, 0, 70;
7: 465, 0, 9660, 0, 19355, 0, 5670, 0;
(End)
LINKS
Andrew Howroyd, Table of n, a(n) for n = 4..30
EXAMPLE
a(4) = 1:
1 1 1 1
1 1 1 1
1 1 1 1
1 1 1 1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jun 12 2008
EXTENSIONS
Terms a(13) and beyond from Andrew Howroyd, Mar 09 2020
STATUS
approved