A200881 Number of 0..3 arrays x(0..n+1) of n+2 elements without any interior element greater than both neighbors.
50, 144, 422, 1268, 3823, 11472, 34350, 102896, 308419, 924532, 2771101, 8305373, 24892609, 74608516, 223618304, 670231838, 2008825312, 6020872062, 18045827096, 54087163859, 162110668160, 485879938474, 1456284886944, 4364793695063
Offset: 1
Keywords
Examples
Some solutions for n=3 ..2....2....2....3....0....3....1....1....3....3....1....3....0....1....3....1 ..0....2....1....2....0....3....1....2....2....3....0....3....1....1....1....2 ..2....1....0....0....2....3....0....2....1....1....1....1....3....0....3....3 ..2....2....0....1....3....3....2....0....2....1....2....0....3....0....3....3 ..0....2....2....2....3....2....3....3....3....2....3....3....1....3....3....3
Links
- R. H. Hardin, Table of n, a(n) for n = 1..210
Formula
Empirical: a(n) = 4*a(n-1) -6*a(n-2) +10*a(n-3) -5*a(n-4) +6*a(n-5) -a(n-6) +a(n-7).
Empirical g.f.: x*(50 - 56*x + 146*x^2 - 56*x^3 + 93*x^4 - 12*x^5 + 16*x^6) / (1 - 4*x + 6*x^2 - 10*x^3 + 5*x^4 - 6*x^5 + x^6 - x^7). - Colin Barker, Oct 16 2017
Comments