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A200888 Number of 0..n arrays x(0..4) of 5 elements without any interior element greater than both neighbors. 1
21, 121, 422, 1121, 2507, 4977, 9052, 15393, 24817, 38313, 57058, 82433, 116039, 159713, 215544, 285889, 373389, 480985, 611934, 769825, 958595, 1182545, 1446356, 1755105, 2114281, 2529801, 3008026, 3555777, 4180351, 4889537, 5691632, 6595457 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Row 3 of A200886.

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..210

FORMULA

Empirical: a(n) = (2/15)*n^5 + (11/6)*n^4 + (35/6)*n^3 + (23/3)*n^2 + (68/15)*n + 1.

Conjectures from Colin Barker, Oct 16 2017: (Start)

G.f.: x*(21 - 5*x + 11*x^2 - 16*x^3 + 6*x^4 - x^5) / (1 - x)^6.

a(n) = 6*a(n-1) - 15*a(n-2) + 20*a(n-3) - 15*a(n-4) + 6*a(n-5) - a(n-6) for n>6.

(End)

EXAMPLE

Some solutions for n=3

..3....3....3....2....0....1....0....3....1....3....3....2....2....2....0....2

..3....3....3....2....1....1....0....3....0....2....1....2....1....3....1....2

..3....3....2....3....1....0....0....2....0....3....3....0....0....3....1....2

..3....3....1....3....0....2....2....3....2....3....3....2....3....1....0....0

..2....0....1....2....3....2....3....3....3....3....0....2....3....2....1....0

CROSSREFS

Sequence in context: A044353 A044734 A325484 * A179441 A164785 A179956

Adjacent sequences:  A200885 A200886 A200887 * A200889 A200890 A200891

KEYWORD

nonn

AUTHOR

R. H. Hardin, Nov 23 2011

STATUS

approved

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Last modified May 27 08:12 EDT 2022. Contains 354096 sequences. (Running on oeis4.)