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 A203493 #7 Jul 22 2025 17:17:34 %S A203493 3,36,624,9540,170868,3171708,59683122,1152091884,22554305502, %T A203493 446374660920,8921216076156,179685599410440,3642895093030506, %U A203493 74273800555695024,1521731710882139544,31310362607335978500 %N A203493 Number of 3Xn 0..2 arrays with row sums equal and column sums unequal to adjacent columns. %C A203493 Row 3 of A203491 %H A203493 R. H. Hardin, <a href="/A203493/b203493.txt">Table of n, a(n) for n = 1..50</a> %e A203493 Some solutions for n=5 %e A203493 ..2..1..2..1..1....0..2..2..2..0....2..2..1..0..0....2..0..1..2..1 %e A203493 ..1..1..2..1..2....1..2..0..1..2....0..0..1..2..2....2..1..2..1..0 %e A203493 ..2..1..1..1..2....2..1..0..2..1....0..1..2..0..2....2..1..1..2..0 %K A203493 nonn %O A203493 1,1 %A A203493 _R. H. Hardin_ Jan 02 2012