A220643 Number of ways to reciprocally link elements of an n X 7 array either to themselves or to exactly one king-move neighbor.

1, 21, 13152, 3725843, 1299348473, 431408410784, 145000880411157, 48590896359378961, 16295162098717276928, 5463664833842177843423, 1832013557267266441097285, 614283122531442244792501056, 205972692517470174457341794041, 69063792561944299889152684046621

Offset

0,2

Links

Alois P. Heinz, Table of n, a(n) for n = 0..200 (terms n = 1..135 from R. H. Hardin)

Example

Some solutions for n=3 0=self 1=nw 2=n 3=ne 4=w 6=e 7=sw 8=s 9=se (reciprocal directions total 10)
..0..0..0..0..0..7..0....0..0..9..6..4..0..0....0..6..4..0..0..7..0
..6..4..7..9..3..8..0....6..4..9..1..0..7..0....6..4..8..9..3..6..4
..0..3..0..0..1..2..0....0..0..0..1..3..6..4....0..0..2..0..1..0..0

Crossrefs

Column 7 of A220644.

Sequence in context: A203674 A250065 A180769 * A185557 A276513 A167063

Adjacent sequences: A220640 A220641 A220642 * A220644 A220645 A220646

Keyword

nonn

Author

R. H. Hardin, Dec 17 2012

Status

approved