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

1,1

Comments

Column 3 of A200886.

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

Example

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

Crossrefs

Sequence in context: A043474 A044301 A044682 * A235942 A093300 A283392

Adjacent sequences: A200878 A200879 A200880 * A200882 A200883 A200884

Keyword

nonn

Author

R. H. Hardin, Nov 23 2011

Status

approved