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 A223507 #6 Jun 02 2025 08:28:53 %S A223507 216,771,20115,426359,9685063,216562815,4867038759,109246101385, %T A223507 2453094910375,55078160026621,1236680655855829,27767207466078683, %U A223507 623458974380912329,13998557054872762899,314310396038821269603 %N A223507 Petersen graph (3,1) coloring a rectangular array: number of 4Xn 0..5 arrays where 0..5 label nodes of a graph with edges 0,1 0,3 3,5 3,4 1,2 1,4 4,5 2,0 2,5 and every array movement to a horizontal, diagonal or antidiagonal neighbor moves along an edge of this graph, with the array starting at 0. %C A223507 Row 4 of A223504 %H A223507 R. H. Hardin, <a href="/A223507/b223507.txt">Table of n, a(n) for n = 1..210</a> %F A223507 Empirical: a(n) = 25*a(n-1) +a(n-2) -1509*a(n-3) +3743*a(n-4) +21956*a(n-5) -87188*a(n-6) -23069*a(n-7) +409623*a(n-8) -235845*a(n-9) -749323*a(n-10) +679813*a(n-11) +599294*a(n-12) -680632*a(n-13) -199246*a(n-14) +294548*a(n-15) +14686*a(n-16) -53558*a(n-17) +3396*a(n-18) +3220*a(n-19) -192*a(n-20) -64*a(n-21) for n>22 %e A223507 Some solutions for n=3 %e A223507 ..0..1..4....0..1..2....0..2..0....0..1..2....0..3..4....0..2..0....0..3..0 %e A223507 ..4..1..2....4..1..0....0..2..1....0..1..2....5..3..5....0..2..0....0..3..4 %e A223507 ..2..1..4....4..3..4....5..2..0....4..1..2....0..2..5....5..2..5....0..1..4 %e A223507 ..4..1..2....0..1..0....1..2..5....4..5..2....5..3..5....0..2..1....2..1..4 %K A223507 nonn %O A223507 1,1 %A A223507 _R. H. Hardin_ Mar 21 2013