This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A220687 #6 Jul 23 2025 01:22:01 %S A220687 1,1081,362057,128995678,42362190063,14108684022136,4701615485821782, %T A220687 1566852499542855296,522108399243273023731,173978947909208417520148, %U A220687 57974051497341052095013087,19318375776055542860988503113 %N A220687 Number of ways to reciprocally link elements of an nX7 array either to themselves or to exactly two horizontal, vertical or antidiagonal neighbors. %C A220687 Column 7 of A220688 %H A220687 R. H. Hardin, <a href="/A220687/b220687.txt">Table of n, a(n) for n = 1..114</a> %e A220687 Some solutions for n=3 0=self 2=n 3=ne 4=w 6=e 7=sw 8=s (reciprocal directions total 10) %e A220687 .00.00.67.46.46.47.00...00.00.00.00.68.48.00...00.00.68.48.68.46.48 %e A220687 .00.36.46.47.37.67.47...00.67.48.00.27.26.47...00.78.28.28.26.47.28 %e A220687 .00.00.36.34.36.34.00...36.46.24.36.46.34.00...36.24.26.24.36.46.24 %K A220687 nonn %O A220687 1,2 %A A220687 _R. H. Hardin_ Dec 17 2012