A248456 Number of length n+2 0..3 arrays with no three consecutive terms having the sum of any two elements equal to twice the third.
48, 148, 460, 1436, 4488, 14040, 43940, 137532, 430508, 1347652, 4218704, 13206360, 41341772, 129418260, 405137308, 1268262348, 3970233208, 12428621208, 38907193300, 121797075276, 381279818252, 1193577924020, 3736437636672
Offset: 1
Keywords
Examples
Some solutions for n=6: ..0....0....0....1....0....2....2....2....2....3....3....1....2....2....0....2 ..3....1....3....1....3....3....1....0....3....0....3....1....2....2....3....2 ..1....3....1....3....3....0....1....3....3....3....1....0....3....0....2....1 ..3....3....3....0....1....0....3....0....2....0....1....1....0....2....0....1 ..1....1....0....0....0....3....1....2....3....1....2....0....3....3....0....2 ..3....0....3....3....3....3....3....3....3....0....1....0....0....0....2....2 ..1....1....0....0....1....0....1....0....2....3....2....2....0....3....0....1 ..1....3....2....1....0....0....3....0....2....0....2....2....1....0....2....1
Links
- R. H. Hardin, Table of n, a(n) for n = 1..210
Crossrefs
Column 3 of A248461.
Formula
Empirical: a(n) = 2*a(n-1) + 3*a(n-2) + 4*a(n-3) - 3*a(n-4) - 12*a(n-5) - 4*a(n-6).
Empirical g.f.: 4*x*(12 + 13*x + 5*x^2 - 30*x^3 - 53*x^4 - 16*x^5) / (1 - 2*x - 3*x^2 - 4*x^3 + 3*x^4 + 12*x^5 + 4*x^6). - Colin Barker, Nov 08 2018
Comments