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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
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
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
KEYWORD
nonn
AUTHOR
R. H. Hardin Dec 18 2012
STATUS
approved