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 A194780 #6 Jul 22 2025 12:36:21 %S A194780 3,17,105,672,4490,31466,231445,1784788,14404218,121421075,1066906979, %T A194780 9753108510,92586250999,911156724048 %N A194780 Number of lower triangles of a (2n)X(2n) 0..n array with new values introduced in row major order 0..n and no element unequal to more than one horizontal or vertical neighbor. %C A194780 Row 2 of A194778 %e A194780 All solutions for n=2 containing a 2 %e A194780 ..0........0........0........0........0 %e A194780 ..0.0......1.1......1.1......0.1......1.1 %e A194780 ..1.1.1....1.1.1....1.1.2....0.1.1....1.1.1 %e A194780 ..1.1.1.2..1.1.1.2..1.1.2.2..0.1.1.2..2.2.2.2 %K A194780 nonn %O A194780 1,1 %A A194780 _R. H. Hardin_ Sep 02 2011