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A333888
Number of non-isomorphic n X n nonnegative integer symmetric matrices with all row and column sums equal to 3 up to permutations of rows and columns.
1
1, 1, 2, 5, 12, 29, 79, 225, 677, 2141, 7121, 24693, 89117, 333312, 1288949, 5140039, 21094565, 88931387, 384544989, 1703083332, 7715920544, 35720666818, 168809971994, 813633173238, 3996247863791, 19986651995983, 101715962631912, 526405121697307, 2768690275913665, 14791474244527076, 80224577967948446
OFFSET
0,3
EXAMPLE
The a(2) = 2 matrices are:
[0 3] [1 2]
[3 0] [2 1]
CROSSREFS
Column k=3 of A333737.
Sequence in context: A261234 A368984 A324787 * A228516 A101411 A042789
KEYWORD
nonn
AUTHOR
Andrew Howroyd, Apr 08 2020
STATUS
approved