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A255661 Number of length n+1 0..3 arrays with at most two downsteps in every n consecutive neighbor pairs. 1
16, 64, 255, 968, 3340, 10320, 28722, 72920, 171106, 375388, 777452, 1532064, 2891360, 5253680, 9231663, 15745452, 26148180, 42392440, 67248205, 104584680, 159730860, 239932160, 354923400, 517641696, 745106454, 1059497716, 1489468594 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Row 1 of A255660.

LINKS

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

FORMULA

Empirical: a(n) = (1/39916800)*n^11 + (1/518400)*n^10 + (1/15120)*n^9 + (137/120960)*n^8 + (12461/1209600)*n^7 + (8251/172800)*n^6 + (56011/362880)*n^5 + (14791/25920)*n^4 + (278149/151200)*n^3 + (8149/2100)*n^2 + (2539/462)*n + 4.

Empirical g.f.: x*(16 - 128*x + 543*x^2 - 1388*x^3 + 2394*x^4 - 2964*x^5 + 2683*x^6 - 1760*x^7 + 814*x^8 - 252*x^9 + 47*x^10 - 4*x^11) / (1 - x)^12. - Colin Barker, Jan 21 2018

EXAMPLE

Some solutions for n=4:

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

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

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

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

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

CROSSREFS

Cf. A255660.

Sequence in context: A212506 A212512 A317235 * A073718 A230970 A061449

Adjacent sequences:  A255658 A255659 A255660 * A255662 A255663 A255664

KEYWORD

nonn

AUTHOR

R. H. Hardin, Mar 01 2015

STATUS

approved

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Last modified October 26 05:58 EDT 2021. Contains 348257 sequences. (Running on oeis4.)