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 A297803 #4 Jan 06 2018 09:33:31 %S A297803 1,4,37,100,293,1320,6215,24879,99567,422308,1804127,7556513,31570236, %T A297803 132859288,559967531,2354250563,9891690637,41598759825,174990998789, %U A297803 735895232858,3094315102349,13012504569964,54724162019621 %N A297803 Number of 3Xn 0..1 arrays with every 1 horizontally, diagonally or antidiagonally adjacent to 2, 3 or 5 neighboring 1s. %C A297803 Row 3 of A297802. %H A297803 R. H. Hardin, <a href="/A297803/b297803.txt">Table of n, a(n) for n = 1..210</a> %F A297803 Empirical: a(n) = 4*a(n-1) -4*a(n-2) +19*a(n-3) +32*a(n-4) -91*a(n-5) -260*a(n-7) -403*a(n-8) +590*a(n-9) +467*a(n-10) +69*a(n-11) -380*a(n-12) -48*a(n-13) -115*a(n-14) +216*a(n-15) +359*a(n-16) +36*a(n-17) -221*a(n-18) -89*a(n-19) -5*a(n-20) +12*a(n-21) %e A297803 Some solutions for n=7 %e A297803 ..1..1..0..0..0..1..0. .0..0..0..1..1..1..0. .0..0..0..1..1..1..0 %e A297803 ..1..1..0..0..1..0..1. .1..1..1..0..0..1..1. .0..1..1..0..1..0..1 %e A297803 ..0..1..1..1..0..1..0. .0..1..1..0..1..1..0. .1..1..0..0..0..1..0 %Y A297803 Cf. A297802. %K A297803 nonn %O A297803 1,2 %A A297803 _R. H. Hardin_, Jan 06 2018