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

1,1

Comments

Limit n->infinity a(n)^(1/n) = 49.36188601343236732586002276917911067895959865... (root of polynomial of degree 50, see the denominator of generating function). - Vaclav Kotesovec, Nov 19 2014

Links

Muhammad Kholilurrohman, Table of n, a(n) for n = 1..300

Vaclav Kotesovec, Generating function and recurrence (of order 90)

Example

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.

Crossrefs

Cf. A239688, A247106.

Sequence in context: A373055 A063836 A172811 * A140441 A261385 A071881

Adjacent sequences: A247067 A247068 A247069 * A247071 A247072 A247073

Keyword

nonn

Author

Muhammad Kholilurrohman, Nov 16 2014

Status

approved