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A220740 Number of ways to reciprocally link elements of an 3Xn array either to themselves or to exactly two horizontal, diagonal and antidiagonal neighbors, without consecutive collinear links 1
1, 4, 22, 103, 487, 2276, 10653, 49951, 234006, 1096844, 5140867, 24096269, 112943160, 529386957, 2481335981, 11630503852, 54514395378, 255519475371, 1197668846683, 5613704209364, 26312510476977, 123331794880035 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Row 3 of A220738

LINKS

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

FORMULA

Empirical: a(n) = 3*a(n-1) +11*a(n-2) -9*a(n-3) -25*a(n-4) -9*a(n-5) +13*a(n-6) +48*a(n-7) +76*a(n-8) -54*a(n-9) -148*a(n-10) +66*a(n-11) -52*a(n-12) -12*a(n-13) +105*a(n-14) -43*a(n-15) +27*a(n-16) +a(n-17) -5*a(n-18) +a(n-19) -a(n-20)

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...00.79.00...00.00.00...69.49.00...00.00.00...00.79.00...00.69.47

.39.00.17...39.67.14...69.47.00...69.14.17...00.67.47...36.47.17...00.39.17

.00.13.00...36.14.00...36.14.00...00.13.00...36.34.00...36.34.00...00.36.14

CROSSREFS

Sequence in context: A254861 A088581 A017970 * A099013 A184510 A184701

Adjacent sequences:  A220737 A220738 A220739 * A220741 A220742 A220743

KEYWORD

nonn

AUTHOR

R. H. Hardin Dec 18 2012

STATUS

approved

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Last modified October 21 21:25 EDT 2021. Contains 348155 sequences. (Running on oeis4.)