A220613 Number of ways to reciprocally link elements of an nX7 array either to themselves or to exactly two horizontal and vertical neighbors, without consecutive collinear links

1, 21, 85, 781, 4673, 34981, 233265, 1653229, 11354857, 79290645, 548972737, 3817993565, 26491584361, 184040357765, 1277739038129, 8873937621293, 61619077914745, 427911161639829, 2971470559369153, 20634790487757629

Offset

1,2

Comments

Column 7 of A220614

Links

R. H. Hardin, Table of n, a(n) for n = 1..210

Formula

Empirical: a(n) = 5*a(n-1) +40*a(n-2) -144*a(n-3) -532*a(n-4) +1484*a(n-5) +3044*a(n-6) -6644*a(n-7) -8872*a(n-8) +13920*a(n-9) +13824*a(n-10) -13056*a(n-11) -10688*a(n-12) +4288*a(n-13) +3072*a(n-14)

Example

Some solutions for n=3 0=self 2=n 4=w 6=e 8=s (reciprocal directions total 10)
.68.48.00.68.48.00.00...68.48.68.48.00.00.00...00.00.00.68.48.00.00
.26.24.00.26.24.00.00...26.24.26.24.00.68.48...00.00.00.26.24.68.48
.00.00.00.00.00.00.00...00.00.00.00.00.26.24...00.00.00.00.00.26.24

Crossrefs

Sequence in context: A041858 A217549 A063651 * A045016 A171129 A301540

Adjacent sequences: A220610 A220611 A220612 * A220614 A220615 A220616

Keyword

nonn

Author

R. H. Hardin Dec 17 2012

Status

approved