a(n) = number of 3-regular (trivalent) multi-graphs without loops on 2n vertices; a(n) = number of symmetric 2n X 2n matrices with {0,1,2,3}-entries with row sum equal to 3 for each row and trace 0.

A108243

a(n) = number of 3-regular (trivalent) multi-graphs without loops on 2n vertices; a(n) = number of symmetric 2n X 2n matrices with {0,1,2,3}-entries with row sum equal to 3 for each row and trace 0.