A220728 Number of ways to reciprocally link elements of an 4Xn array either to themselves or to exactly two horizontal, diagonal or antidiagonal neighbors

1, 8, 126, 2586, 52189, 1071230, 21914482, 449023031, 9196824619, 188399767218, 3859260231149, 79056143231850, 1619440886287615, 33173815285042631, 679556410727542259, 13920527633029367143, 285158193122827850868

Offset

1,2

Comments

Row 4 of A220725

Links

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

Formula

Empirical: a(n) = 20*a(n-1) +55*a(n-2) -913*a(n-3) -294*a(n-4) +1396*a(n-5) +6052*a(n-6) +11468*a(n-7) -1929*a(n-8) -29156*a(n-9) -69229*a(n-10) +5550*a(n-11) +77439*a(n-12) +61760*a(n-13) -10148*a(n-14) -26093*a(n-15) -24390*a(n-16) -1213*a(n-17) +12028*a(n-18) -1380*a(n-19) +1823*a(n-20) -1197*a(n-21) +66*a(n-22) +47*a(n-23) -13*a(n-24) +2*a(n-25)

Example

Some solutions for n=3 0=self 1=nw 3=ne 4=w 6=e 7=sw 9=se (reciprocal directions total 10)
.00.79.00...00.69.47...69.47.00...69.49.00...00.67.47...69.49.00...00.79.00
.36.46.14...00.36.14...36.14.00...00.16.14...36.34.00...00.17.17...36.46.14
.00.69.47...69.49.00...69.49.00...00.79.00...69.47.00...39.39.00...69.46.47
.00.36.14...00.16.14...00.16.14...36.46.14...36.14.00...00.16.14...00.13.00

Crossrefs

Sequence in context: A236549 A360852 A262732 * A355766 A029472 A001081

Adjacent sequences: A220725 A220726 A220727 * A220729 A220730 A220731

Keyword

nonn

Author

R. H. Hardin Dec 18 2012

Status

approved