A198316 Number of, not necessarily connected, regular simple graphs on n vertices with girth exactly 6.
0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 1, 2, 1, 2, 1, 7, 2, 35, 3, 389, 4, 7579, 6, 181233, 9, 4624493, 12, 122090019, 17, 3328899632, 24, 93988911093, 57
Offset: 0