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 A207312 #7 Jul 22 2025 20:17:28 %S A207312 26,676,15390,347502,7791488,174545777,3908531208,87515884741, %T A207312 1959513380192,43873997112932,982347997376840,21994968695108692, %U A207312 492471697249839464,11026538323840183371,246886363177103814747 %N A207312 Number of nX3 0..2 arrays avoiding the pattern z-2 z-1 z in any row, column or nw-to-se diagonal. %C A207312 Column 3 of A207317 %H A207312 R. H. Hardin, <a href="/A207312/b207312.txt">Table of n, a(n) for n = 1..210</a> %F A207312 Empirical: a(n) = 27*a(n-1) -43*a(n-2) -1591*a(n-3) +4195*a(n-4) +31861*a(n-5) -81210*a(n-6) -248372*a(n-7) +529289*a(n-8) +552322*a(n-9) -1158991*a(n-10) -641935*a(n-11) +1301158*a(n-12) +424638*a(n-13) -829889*a(n-14) -156675*a(n-15) +298360*a(n-16) +28115*a(n-17) -53314*a(n-18) -1015*a(n-19) +2751*a(n-20) +80*a(n-21) -64*a(n-22) %e A207312 Some solutions for n=4 %e A207312 ..2..0..1....2..1..2....1..2..1....2..1..0....2..0..2....1..0..1....2..2..1 %e A207312 ..0..0..2....1..2..1....1..1..1....0..1..1....1..1..1....2..0..2....2..0..0 %e A207312 ..1..1..2....0..2..1....1..0..1....1..0..0....1..0..0....0..2..2....2..0..0 %e A207312 ..0..0..1....1..1..2....2..1..2....1..2..2....1..2..2....2..0..2....2..2..2 %K A207312 nonn %O A207312 1,1 %A A207312 _R. H. Hardin_ Feb 16 2012