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, 4, 22, 103, 487, 2276, 10653, 49951, 234006, 1096844, 5140867, 24096269, 112943160, 529386957, 2481335981, 11630503852, 54514395378, 255519475371, 1197668846683, 5613704209364, 26312510476977, 123331794880035

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