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 A301536 #6 May 20 2021 12:37:59 %S A301536 3,6,9,26,61,154,374,941,2357,5963,15074,38168,96641,244836,620311, %T A301536 1571854,3983147,10093850,25579490,64823479,164276135,416311227, %U A301536 1055023990,2673664936,6775663297,17171047596,43515284891,110277499816 %N A301536 Number of n X 3 0..1 arrays with every element equal to 0, 1 or 3 horizontally or vertically adjacent elements, with upper left element zero. %C A301536 Column 3 of A301541. %H A301536 R. H. Hardin, <a href="/A301536/b301536.txt">Table of n, a(n) for n = 1..210</a> %F A301536 Empirical: a(n) = 3*a(n-1) -a(n-2) -a(n-3) +2*a(n-4) -a(n-5) +3*a(n-6) -11*a(n-7) -a(n-8) +2*a(n-9) -4*a(n-10) -2*a(n-11) -a(n-12) +11*a(n-13) +3*a(n-14) +a(n-15) +2*a(n-16) +a(n-17) -a(n-18) -3*a(n-19) -a(n-20). %e A301536 Some solutions for n=5 %e A301536 ..0..1..0. .0..1..0. .0..1..0. .0..1..0. .0..0..0. .0..1..0. .0..1..0 %e A301536 ..1..0..1. .1..0..1. .1..0..1. .0..0..0. .1..0..1. .1..0..1. .1..0..1 %e A301536 ..0..1..0. .1..1..1. .0..1..1. .0..0..0. .1..1..0. .1..0..1. .0..1..1 %e A301536 ..1..0..0. .1..1..1. .1..0..1. .0..1..0. .1..0..0. .0..1..0. .1..0..1 %e A301536 ..0..1..0. .1..0..1. .0..1..0. .1..0..1. .0..1..0. .0..1..0. .0..0..0 %Y A301536 Cf. A301541. %K A301536 nonn %O A301536 1,1 %A A301536 _R. H. Hardin_, Mar 23 2018