A220712 Number of ways to reciprocally link elements of an 7Xn array either to themselves or to exactly two horizontal and antidiagonal neighbors, without consecutive collinear links.

1, 1, 21, 129, 932, 6412, 44976, 311193, 2168111, 15034974, 104478616, 725286308, 5037269200, 34977393156, 242898931716, 1686719471828, 11713075485508, 81338093590180, 564832581201972, 3922330554994484, 27237632538545092

Offset: 1

Author

R. H. Hardin Dec 18 2012

Keywords

• nonn

Comments

Row 7 of A220708

Examples

			Some solutions for n=3 0=self 3=ne 4=w 6=e 7=sw (reciprocal directions total 10)
.00.67.47...00.00.00...00.00.00...00.67.47...00.67.47...00.67.47...00.00.00
.36.34.00...00.00.00...00.67.47...36.34.00...36.34.00...36.34.00...00.00.00
.00.00.00...00.67.47...36.34.00...00.67.47...00.67.47...00.67.47...00.67.47
.00.00.00...36.34.00...00.00.00...36.34.00...36.34.00...36.34.00...36.34.00
.00.00.00...00.00.00...00.67.47...00.00.00...00.00.00...00.67.47...00.00.00
.00.00.00...00.00.00...36.34.00...00.67.47...00.00.00...36.34.00...00.67.47
.00.00.00...00.00.00...00.00.00...36.34.00...00.00.00...00.00.00...36.34.00
		

Links

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

Formula

Empirical: a(n) = a(n-1) +76*a(n-2) -4*a(n-3) -2156*a(n-4) -520*a(n-5) +32432*a(n-6) +9800*a(n-7) -296352*a(n-8) -80128*a(n-9) +1755472*a(n-10) +365536*a(n-11) -6970672*a(n-12) -1003248*a(n-13) [phone]*a(n-14) +1679040*a(n-15) -34716928*a(n-16) -1650048*a(n-17) [phone]*a(n-18) +820736*a(n-19) -35163136*a(n-20) -61440*a(n-21) [phone]*a(n-22) -116736*a(n-23) -5017600*a(n-24) +36864*a(n-25) +589824*a(n-26) for n>32