cp's OEIS Frontend

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

%I A220620 #6 Jul 23 2025 01:18:20
%S A220620 21,4565,624227,93905509,13864972277,2054706174413,304265433695569,
%T A220620 45062687311719797,6673721691080067317,988374130647554935157,
%U A220620 146377412047334158410357,21678380394232186381827093
%N A220620 Number of ways to reciprocally link elements of an nX7 array either to themselves or to exactly one horizontal, diagonal and antidiagonal neighbor.
%C A220620 Column 7 of A220621
%H A220620 R. H. Hardin, <a href="/A220620/b220620.txt">Table of n, a(n) for n = 1..210</a>
%F A220620 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) +24279361760*a(n-7) +198170224768*a(n-8) -2875481635520*a(n-9) -383756692624*a(n-10) +115334410373680*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) +6240587481088*a(n-36) -274877906944*a(n-37)
%e A220620 Some solutions for n=3 0=self 1=nw 3=ne 4=w 6=e 7=sw 9=se (reciprocal directions total 10)
%e A220620 ..0..7..9..0..0..0..7....0..7..6..4..6..4..0....0..7..0..0..0..9..0
%e A220620 ..3..0..7..1..7..3..0....3..0..0..0..0..6..4....3..0..9..9..6..4..1
%e A220620 ..0..3..0..3..6..4..0....6..4..0..0..0..0..0....0..6..4..1..1..0..0
%K A220620 nonn
%O A220620 1,1
%A A220620 _R. H. Hardin_ Dec 17 2012