A221521 Number of 0..5 arrays of length n with each element differing from at least one neighbor by 2 or more.
0, 20, 68, 400, 1940, 9982, 50400, 256018, 1297924, 6584320, 33394958, 169387004, 859152000, 4357755890, 22103183110, 112110699524, 568642349004, 2884239836106, 14629299498936, 74202014273586, 376363810775194
Offset: 1
Keywords
Examples
Some solutions for n=6 ..2....4....0....4....2....0....0....5....2....1....2....0....0....0....4....5 ..5....2....5....0....5....5....3....2....5....4....4....4....5....5....0....0 ..2....1....2....1....0....1....1....0....1....1....0....3....0....1....0....3 ..3....4....4....4....4....5....4....2....3....1....2....5....1....3....2....5 ..1....5....4....5....1....1....0....3....1....5....1....5....3....5....1....3 ..4....3....0....1....3....3....2....0....3....3....5....0....5....0....3....1
Links
- R. H. Hardin, Table of n, a(n) for n = 1..210
Formula
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).
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
Comments