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 A198904 #7 Jul 22 2025 13:06:39 %S A198904 51,62004,89793204,130292546801,189062985604305,274342896958292170, %T A198904 398089706066811447174,577654521153750977585383, %U A198904 838214957290859115489996817,1216305402162613228248847610489 %N A198904 Number of nX6 0..4 arrays with values 0..4 introduced in row major order and no element equal to any horizontal or vertical neighbor. %C A198904 Column 6 of A198906 %H A198904 R. H. Hardin, <a href="/A198904/b198904.txt">Table of n, a(n) for n = 1..100</a> %F A198904 Empirical: a(n) = 1941*a(n-1) -806387*a(n-2) +148087843*a(n-3) -14409929271*a(n-4) +778094676063*a(n-5) -21816737058431*a(n-6) +172301552678113*a(n-7) +7343185920165785*a(n-8) -245567930834154099*a(n-9) +3173967512676632848*a(n-10) -15227320856420081570*a(n-11) -91185217544269175883*a(n-12) +1851754850894045611993*a(n-13) -13021262413927953929580*a(n-14) +53026970301996239080604*a(n-15) -137791962761820102384680*a(n-16) +234523646685947458039624*a(n-17) -259529910793881853229984*a(n-18) +179240545997964052307808*a(n-19) -69895831119161489802880*a(n-20) +11699525896373883270144*a(n-21) %e A198904 Some solutions with values 0 to 4 for n=4 %e A198904 ..0..1..0..2..3..4....0..1..0..2..0..3....0..1..0..2..3..0....0..1..0..2..0..3 %e A198904 ..1..0..1..0..2..1....1..0..1..0..3..2....1..0..1..0..4..3....1..0..1..0..3..0 %e A198904 ..0..1..0..2..1..4....0..1..0..3..4..0....0..1..0..2..3..1....0..1..0..3..0..1 %e A198904 ..1..0..1..4..2..0....1..0..1..2..1..4....1..0..1..0..2..0....1..0..1..4..1..4 %K A198904 nonn %O A198904 1,1 %A A198904 _R. H. Hardin_ Oct 31 2011