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 A218422 #6 Jul 22 2025 23:56:43 %S A218422 9,191,2725,41515,629659,9539915,144597047,2191517757,33214850067, %T A218422 503408006597,7629705089721,115636627121941,1752601092641329, %U A218422 26562609636801375,402585753260380041,6101632743611966643 %N A218422 Hilltop maps: number of nX4 binary arrays indicating the locations of corresponding elements not exceeded by any horizontal, vertical or antidiagonal neighbor in a random 0..1 nX4 array. %C A218422 Column 4 of A218426 %H A218422 R. H. Hardin, <a href="/A218422/b218422.txt">Table of n, a(n) for n = 1..146</a> %F A218422 Empirical: a(n) = 9*a(n-1) +72*a(n-2) +284*a(n-3) +526*a(n-4) +890*a(n-5) +902*a(n-6) +1382*a(n-7) -553*a(n-8) +2141*a(n-9) -1904*a(n-10) +416*a(n-11) -53*a(n-12) -263*a(n-13) -38*a(n-14) +38*a(n-15) -6*a(n-16) -18*a(n-17) +16*a(n-18) -a(n-20) +a(n-21) %e A218422 Some solutions for n=3 %e A218422 ..1..1..0..0....1..1..0..1....0..1..0..1....1..1..0..0....0..1..0..1 %e A218422 ..1..0..1..0....0..1..1..1....1..1..1..1....1..0..1..1....1..0..0..1 %e A218422 ..1..1..0..1....0..1..0..0....0..0..1..1....1..0..1..1....0..1..0..0 %K A218422 nonn %O A218422 1,1 %A A218422 _R. H. Hardin_ Oct 28 2012