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 A195243 #9 Jul 22 2025 12:41:56 %S A195243 4,46,1682,190514,67379894,74236765958,254948725307650, %T A195243 2728873272983950594,91038149737139587502854, %U A195243 9466106148769015848820814134,3067809430979519600024270636572850 %N A195243 Number of lower triangles of an n X n 0..3 array with each element differing from all of its diagonal, vertical, antidiagonal and horizontal neighbors by two or less. %C A195243 Column 3 of A195248 %H A195243 R. H. Hardin, <a href="/A195243/b195243.txt">Table of n, a(n) for n = 1..18</a> %e A195243 Some solutions for n=5 %e A195243 ..1..........2..........1..........3..........0..........1..........0 %e A195243 ..0.2........2.1........0.2........1.1........2.1........1.3........2.1 %e A195243 ..2.0.2......2.0.0......2.1.3......1.1.2......0.2.2......3.3.1......0.2.2 %e A195243 ..0.0.1.3....2.1.1.2....0.2.1.3....3.2.1.1....2.1.1.0....3.1.1.3....2.1.1.0 %e A195243 ..0.1.2.3.3..1.2.2.1.0..2.1.3.3.3..2.1.2.2.3..1.0.0.1.2..2.3.2.2.1..1.0.0.1.2 %K A195243 nonn %O A195243 1,1 %A A195243 _R. H. Hardin_ Sep 13 2011