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 A208172 #7 Jul 22 2025 21:13:37 %S A208172 51,33831,26625693,21002874867,16567902881244,13069424064243420, %T A208172 10309684155118737894,8132690993759302714128, %U A208172 6415391762234363693863872,5060717478941101906268770749,3992096250836003074558657203441 %N A208172 Number of nX5 0..3 arrays with new values 0..3 introduced in row major order and no element equal to more than one of its immediate leftward or upward neighbors. %C A208172 Column 5 of A208175 %H A208172 R. H. Hardin, <a href="/A208172/b208172.txt">Table of n, a(n) for n = 1..210</a> %F A208172 Empirical: a(n) = 846*a(n-1) -46537*a(n-2) +1162868*a(n-3) -17173907*a(n-4) +166807056*a(n-5) -1125592122*a(n-6) +5444000730*a(n-7) -19238506974*a(n-8) +50296239144*a(n-9) -97844056164*a(n-10) +140881555908*a(n-11) -146587250745*a(n-12) +104533491168*a(n-13) -46130948685*a(n-14) +10416243600*a(n-15) -863591625*a(n-16) for n>17 %e A208172 Some solutions for n=4 %e A208172 ..0..1..1..0..0....0..0..0..0..0....0..0..0..1..0....0..0..0..0..0 %e A208172 ..0..2..0..1..2....0..1..1..1..0....0..1..1..0..2....1..0..1..0..1 %e A208172 ..1..1..3..1..0....1..2..2..2..1....2..1..2..2..3....1..0..0..2..1 %e A208172 ..0..1..0..2..3....0..0..3..0..0....0..1..3..1..3....2..3..3..0..3 %K A208172 nonn %O A208172 1,1 %A A208172 _R. H. Hardin_ Feb 24 2012