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A255624 Number of length n+2 0..2 arrays with at most two downsteps in every n consecutive neighbor pairs. 1
27, 81, 243, 694, 1803, 4248, 9186, 18483, 35016, 63060, 108774, 180801, 290998, 455313, 694827, 1036980, 1517001, 2179563, 3080685, 4289904, 5892741, 7993486, 10718328, 14218857, 18675966, 24304182, 31356456, 40129443, 50969304, 64278063 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Row 2 of A255622.

LINKS

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

FORMULA

Empirical: a(n) = (1/40320)*n^8 + (13/10080)*n^7 + (59/2880)*n^6 + (61/360)*n^5 + (5167/5760)*n^4 + (901/1440)*n^3 + (17077/3360)*n^2 + (3977/280)*n + 6.

Empirical g.f.: x*(3 - 2*x)*(9 - 48*x + 130*x^2 - 195*x^3 + 171*x^4 - 87*x^5 + 24*x^6 - 3*x^7) / (1 - x)^9. - Colin Barker, Jan 21 2018

EXAMPLE

Some solutions for n=4:

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

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

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

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

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

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

CROSSREFS

Cf. A255622.

Sequence in context: A216438 A292872 A057609 * A008884 A031455 A045004

Adjacent sequences:  A255621 A255622 A255623 * A255625 A255626 A255627

KEYWORD

nonn

AUTHOR

R. H. Hardin, Feb 28 2015

STATUS

approved

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Last modified October 1 13:38 EDT 2022. Contains 357149 sequences. (Running on oeis4.)