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, 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

Links

Table of n, a(n) for n=0..30.

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

Adjacent sequences: A333885 A333886 A333887 * A333889 A333890 A333891

Keyword

nonn

Author

Andrew Howroyd, Apr 08 2020

Status

approved