A358996 Number of self-avoiding paths of length 2*(n+A002620(n-1)) along the edges of a grid with n X n square cells, which do not pass above the diagonal, start at the lower left corner and finish at the upper right corner.

1, 1, 2, 2, 10, 20, 248, 1072, 31178, 270026, 18806964, 329412610, 54393195014, 1931171930256, 749416883107560, 54217060622200086

Offset: 0

Author

Seiichi Manyama, Dec 09 2022

Keywords

• nonn
• more

Examples

			3 X 3 square cells
  *---*---*---E
  |   |   |   |
  *---*---*---*
  |   |   |   |
  *---*---*---*
  |   |   |   |
  S---*---*---*
a(3) = 2;
              E              E
              |              |
              *          *---*
              |          |
      *---*   *          *---*
      |   |   |              |
  S---*   *---*  S---*---*---*
		

Crossrefs

Cf. A000108, A002620, A340005, A340043.

Formula

a(n) = A340043(n, A002620(n-1)).