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A255109
Number of length n+2 0..2 arrays with at most one downstep in every n consecutive neighbor pairs.
1
27, 75, 168, 331, 597, 1008, 1616, 2484, 3687, 5313, 7464, 10257, 13825, 18318, 23904, 30770, 39123, 49191, 61224, 75495, 92301, 111964, 134832, 161280, 191711, 226557, 266280, 311373, 362361, 419802, 484288, 556446, 636939, 726467, 825768, 935619
OFFSET
1,1
COMMENTS
Row 2 of A255107.
LINKS
FORMULA
Empirical: a(n) = (1/120)*n^5 + (5/24)*n^4 + (37/24)*n^3 + (175/24)*n^2 + (239/20)*n + 6.
Empirical g.f.: x*(3 - 3*x + x^2)*(9 - 20*x + 18*x^2 - 6*x^3) / (1 - x)^6. - Colin Barker, Jan 24 2018
EXAMPLE
Some solutions for n=4:
0 2 2 0 2 2 1 0 0 1 1 1 1 2 2 2
0 2 0 1 0 2 1 0 2 1 0 1 1 1 0 2
0 1 2 0 1 2 1 0 0 2 0 2 0 1 1 0
1 1 2 1 2 0 0 2 0 1 0 2 0 1 1 0
0 1 2 2 2 2 1 2 0 1 2 1 1 1 2 0
1 1 2 2 2 2 2 2 1 2 1 2 1 2 2 1
CROSSREFS
Cf. A255107.
Sequence in context: A325824 A163506 A226357 * A369063 A297326 A044165
KEYWORD
nonn
AUTHOR
R. H. Hardin, Feb 14 2015
STATUS
approved