cp's OEIS Frontend

A221521 Number of 0..5 arrays of length n with each element differing from at least one neighbor by 2 or more.

%I A221521 #9 Oct 18 2017 13:28:47
%S A221521 0,20,68,400,1940,9982,50400,256018,1297924,6584320,33394958,
%T A221521 169387004,859152000,4357755890,22103183110,112110699524,568642349004,
%U A221521 2884239836106,14629299498936,74202014273586,376363810775194
%N A221521 Number of 0..5 arrays of length n with each element differing from at least one neighbor by 2 or more.
%C A221521 Column 5 of A221524.
%H A221521 R. H. Hardin, <a href="/A221521/b221521.txt">Table of n, a(n) for n = 1..210</a>
%F A221521 Empirical: a(n) = 2*a(n-1) +11*a(n-2) +20*a(n-3) +17*a(n-4) -3*a(n-5) +a(n-6).
%F A221521 Empirical g.f.: 2*x^2*(10 + 14*x + 22*x^2 - 4*x^3 + x^4) / (1 - 2*x - 11*x^2 - 20*x^3 - 17*x^4 + 3*x^5 - x^6). - _Colin Barker_, Oct 18 2017
%e A221521 Some solutions for n=6
%e A221521 ..2....4....0....4....2....0....0....5....2....1....2....0....0....0....4....5
%e A221521 ..5....2....5....0....5....5....3....2....5....4....4....4....5....5....0....0
%e A221521 ..2....1....2....1....0....1....1....0....1....1....0....3....0....1....0....3
%e A221521 ..3....4....4....4....4....5....4....2....3....1....2....5....1....3....2....5
%e A221521 ..1....5....4....5....1....1....0....3....1....5....1....5....3....5....1....3
%e A221521 ..4....3....0....1....3....3....2....0....3....3....5....0....5....0....3....1
%K A221521 nonn
%O A221521 1,2
%A A221521 _R. H. Hardin_, Jan 19 2013