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 A208256 #7 Jul 22 2025 21:15:13 %S A208256 122,49152,19566912,7782199824,3094987890864,1230875651548608, %T A208256 489518751475118880,194681408759751734640,77424717204435400421520, %U A208256 30791778589670316720418080,12245877840416847143166208896 %N A208256 Number of nX6 0..2 arrays with new values 0..2 introduced in row major order and no element equal to more than one of its immediate leftward or upward neighbors. %C A208256 Column 6 of A208258 %H A208256 R. H. Hardin, <a href="/A208256/b208256.txt">Table of n, a(n) for n = 1..210</a> %F A208256 Empirical: a(n) = 483*a(n-1) -37260*a(n-2) +1406078*a(n-3) -32825379*a(n-4) +522499249*a(n-5) -5935275892*a(n-6) +48955308778*a(n-7) -292045494268*a(n-8) +1227794612112*a(n-9) -3438890819616*a(n-10) +5747863337984*a(n-11) -4538037229568*a(n-12) +808526872576*a(n-13) +1304252383232*a(n-14) -1133951057920*a(n-15) +395539644416*a(n-16) -52613349376*a(n-17) for n>18 %e A208256 Some solutions for n=4 %e A208256 ..0..1..0..2..1..2....0..1..1..2..0..2....0..0..1..2..0..2....0..0..0..0..1..0 %e A208256 ..2..1..1..0..1..1....2..0..1..1..0..1....1..0..2..1..2..1....0..1..2..1..0..1 %e A208256 ..0..0..2..0..0..2....1..1..2..1..0..0....2..2..1..2..0..2....2..0..0..0..2..0 %e A208256 ..0..1..0..1..2..0....0..1..2..1..0..2....2..0..0..0..2..1....0..1..1..1..0..1 %K A208256 nonn %O A208256 1,1 %A A208256 _R. H. Hardin_ Feb 24 2012