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 A207405 #7 Jul 22 2025 20:22:53 %S A207405 10,100,390,1521,4212,11664,26676,61009,123006,248004,456666,840889, %T A207405 1445192,2483776,4042440,6579225,10244610,15952036,23944030,35940025, %U A207405 52300380,76108176,107854812,152843769,211679286,293162884,397932402 %N A207405 Number of 5Xn 0..1 arrays avoiding 0 0 1 and 0 1 1 horizontally and 0 0 1 and 1 1 0 vertically. %C A207405 Row 5 of A207403 %H A207405 R. H. Hardin, <a href="/A207405/b207405.txt">Table of n, a(n) for n = 1..210</a> %F A207405 Empirical: a(n) = 2*a(n-1) +8*a(n-2) -18*a(n-3) -27*a(n-4) +72*a(n-5) +48*a(n-6) -168*a(n-7) -42*a(n-8) +252*a(n-9) -252*a(n-11) +42*a(n-12) +168*a(n-13) -48*a(n-14) -72*a(n-15) +27*a(n-16) +18*a(n-17) -8*a(n-18) -2*a(n-19) +a(n-20) %e A207405 Some solutions for n=4 %e A207405 ..0..0..0..0....1..1..0..0....0..0..0..0....1..0..1..0....1..1..0..0 %e A207405 ..1..0..0..0....0..0..0..0....0..1..0..0....0..1..0..0....1..1..1..0 %e A207405 ..0..0..0..0....1..0..0..0....0..0..0..0....0..1..0..0....1..1..1..0 %e A207405 ..0..0..0..0....0..0..0..0....0..0..0..0....0..1..0..0....1..1..1..0 %e A207405 ..0..0..0..0....0..0..0..0....0..0..0..0....0..1..0..0....1..1..1..0 %K A207405 nonn %O A207405 1,1 %A A207405 _R. H. Hardin_ Feb 17 2012