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 A221448 #6 Jul 23 2025 01:56:29 %S A221448 1,31,221,1465,10593,76055,543081,3883061,27769277,198564543, %T A221448 1419847869,10152784401,72598518713,519122981715,3712041493221, %U A221448 26543328598837,189800757263741,1357189525524527,9704721072833461,69394590298217165 %N A221448 Hilltop maps: number of 3Xn binary arrays indicating the locations of corresponding elements not exceeded by any horizontal or antidiagonal neighbor in a random 0..1 3Xn array. %C A221448 Row 3 of A221446 %H A221448 R. H. Hardin, <a href="/A221448/b221448.txt">Table of n, a(n) for n = 1..210</a> %F A221448 Empirical: a(n) = 5*a(n-1) +8*a(n-2) +46*a(n-3) +39*a(n-4) +69*a(n-5) -10*a(n-6) -38*a(n-7) -68*a(n-8) -40*a(n-9) +50*a(n-10) +18*a(n-11) -13*a(n-12) -7*a(n-13) +4*a(n-14) +2*a(n-15) -a(n-16) +a(n-17) %e A221448 Some solutions for n=3 %e A221448 ..0..1..1....1..1..0....1..1..1....1..1..1....0..1..0....0..1..1....1..0..1 %e A221448 ..1..1..0....0..1..1....1..1..1....0..1..1....0..0..1....0..1..1....1..1..1 %e A221448 ..1..0..1....1..1..1....0..1..0....1..1..1....1..1..1....1..0..1....1..1..0 %K A221448 nonn %O A221448 1,2 %A A221448 _R. H. Hardin_ Jan 17 2013