A247070 Number of paths joining opposite corners of an n X 3 grid with every vertex appearing at most twice in the path.
3, 218, 9482, 457712, 22375458, 1103498043, 54446999831, 2687689834743, 132666417488114, 6548713810387879, 323256199668617476, 15956549284724388645, 787645179268653581373, 38879655000676000582023, 1919173045780901708089448
Offset: 1
Keywords
Examples
For n = 1 corresponds to a straight line graph with vertices {1,2,3}. Then the a(1) = 3 solutions are 123, 12123, and 12323.
Links
- Muhammad Kholilurrohman, Table of n, a(n) for n = 1..300
- Vaclav Kotesovec, Generating function and recurrence (of order 90)
Comments