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 A203831 #7 Jul 22 2025 17:32:34 %S A203831 5625,151659,4238721,119606211,3383285769,95763046491,2710984443345, %T A203831 76749227497395,2172829037910489,61514609224652235, %U A203831 1741531281545538081,49304251065416837283,1395845890054082693289,39517602012270762571323 %N A203831 Number of (n+1)X5 0..2 arrays with every 2X2 subblock having equal diagonal elements or equal antidiagonal elements. %C A203831 Column 4 of A203835 %H A203831 R. H. Hardin, <a href="/A203831/b203831.txt">Table of n, a(n) for n = 1..210</a> %F A203831 Empirical: a(n) = 31*a(n-1) -24*a(n-2) -1612*a(n-3) +3816*a(n-4) +1152*a(n-5) -2784*a(n-6) +256*a(n-7) %e A203831 Some solutions for n=4 %e A203831 ..2..1..2..1..0....2..0..2..2..0....1..0..1..2..0....0..0..0..1..2 %e A203831 ..1..2..1..2..1....1..2..1..2..2....1..1..2..0..2....1..0..2..0..1 %e A203831 ..1..1..1..1..2....2..1..0..1..2....2..1..1..2..2....2..1..0..0..0 %e A203831 ..2..1..2..1..1....1..1..1..1..1....2..2..1..1..2....2..2..1..0..0 %e A203831 ..2..2..2..2..1....2..1..1..1..0....2..1..0..1..1....1..2..2..1..0 %K A203831 nonn %O A203831 1,1 %A A203831 _R. H. Hardin_ Jan 06 2012