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 A216457 #6 Jul 22 2025 23:31:51 %S A216457 1,1,7,20,322,1335,36401,192713,7712455,49055292,2659544320, %T A216457 19602119017,1367160898137,11399696350555,986429423363481, %U A216457 9146845346099410,955922762706415420,9731199828137067515,1203020866861467699281 %N A216457 Number of horizontal, diagonal and antidiagonal neighbor colorings of the even squares of an nX3 array with new integer colors introduced in row major order. %C A216457 Column 3 of A216460 %H A216457 R. H. Hardin, <a href="/A216457/b216457.txt">Table of n, a(n) for n = 1..95</a> %e A216457 Some solutions for n=4 %e A216457 ..0..x..1....0..x..1....0..x..1....0..x..1....0..x..1....0..x..1....0..x..1 %e A216457 ..x..2..x....x..2..x....x..2..x....x..2..x....x..2..x....x..2..x....x..2..x %e A216457 ..3..x..4....0..x..1....1..x..3....0..x..3....3..x..4....3..x..4....3..x..1 %e A216457 ..x..1..x....x..2..x....x..4..x....x..2..x....x..0..x....x..2..x....x..0..x %K A216457 nonn %O A216457 1,3 %A A216457 _R. H. Hardin_ Sep 07 2012