A220620 Number of ways to reciprocally link elements of an nX7 array either to themselves or to exactly one horizontal, diagonal and antidiagonal neighbor.

21, 4565, 624227, 93905509, 13864972277, 2054706174413, 304265433695569, 45062687311719797, 6673721691080067317, 988374130647554935157, 146377412047334158410357, 21678380394232186381827093

Offset: 1

Author

R. H. Hardin Dec 17 2012

Keywords

• nonn

Comments

Column 7 of A220621

Examples

			Some solutions for n=3 0=self 1=nw 3=ne 4=w 6=e 7=sw 9=se (reciprocal directions total 10)
..0..7..9..0..0..0..7....0..7..6..4..6..4..0....0..7..0..0..0..9..0
..3..0..7..1..7..3..0....3..0..0..0..0..6..4....3..0..9..9..6..4..1
..0..3..0..3..6..4..0....6..4..0..0..0..0..0....0..6..4..1..1..0..0
		

Links

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

Formula

Empirical: a(n) = 201*a(n-1) -6982*a(n-2) -189430*a(n-3) +9590330*a(n-4) -17036302*a(n-5) -2815039392*a(n-6) [phone]*a(n-7) [phone]*a(n-8) -2875481635520*a(n-9) -383756692624*a(n-10) [phone]*a(n-11) -283314863036560*a(n-12) -1777891655816032*a(n-13) +7541953262286912*a(n-14) +7231319523252480*a(n-15) -67620253084304384*a(n-16) +32587945923607040*a(n-17) +252473367356505600*a(n-18) -301020866429181440*a(n-19) -378989877588835840*a(n-20) +740276347708960768*a(n-21) +102424394439131136*a(n-22) -719256751312953344*a(n-23) +211285473650806784*a(n-24) +277487256139481088*a(n-25) -178573089681702912*a(n-26) -26529867221958656*a(n-27) +59859716422762496*a(n-28) -8012264149876736*a(n-29) -11308640300433408*a(n-30) +1932970382327808*a(n-31) +1107369538879488*a(n-32) -185816928223232*a(n-33) -37457215094784*a(n-34) -13028783292416*a(n-35) [phone]*a(n-36) -274877906944*a(n-37)