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A267227 Number of length-n 0..3 arrays with no following elements greater than or equal to the first repeated value. 1
4, 16, 54, 176, 564, 1790, 5646, 17732, 55512, 173354, 540258, 1680848, 5221740, 16200758, 50204790, 155413724, 480622848, 1484980802, 4584213642, 14140323560, 43583756436, 134239102286, 413179757214, 1270924525556, 3906925144104 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Column 3 of A267232.

LINKS

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

FORMULA

Empirical: a(n) = 9*a(n-1) - 29*a(n-2) + 39*a(n-3) - 18*a(n-4) for n > 5.

Conjectures from Colin Barker, Feb 05 2018: (Start)

G.f.: 2*x*(2 - 10*x + 13*x^2 - x^3 - 3*x^4) / ((1 - x)*(1 - 2*x)*(1 - 3*x)^2).

a(n) = (-9 - 9*2^n + 11*3^(1+n) + 2*3^n*n) / 18 for n>1.

(End)

EXAMPLE

Some solutions for n=6:

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

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

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

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

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

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

CROSSREFS

Cf. A267232.

Sequence in context: A254823 A134968 A238419 * A223944 A127634 A331457

Adjacent sequences:  A267224 A267225 A267226 * A267228 A267229 A267230

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jan 12 2016

STATUS

approved

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Last modified June 12 07:43 EDT 2021. Contains 344943 sequences. (Running on oeis4.)