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A194888 Number of lower triangles of an n X n 0..3 array with new values introduced in row major order 0..3 and no two horizontal or vertical neighbors of any element equal. 1
1, 3, 24, 192, 1152, 5760, 26880, 118272, 506880, 2119680, 8761344, 35807232, 145539072, 588349440, 2372075520, 9538240512, 38303170560, 153613762560, 615659864064, 2465854390272, 9873068654592, 39518019256320, 158149336104960 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Column 3 of A194893.

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..24

FORMULA

Empirical (for n>=3): 9*2^(2*n-2) - (1-(-1)^n)*21/8*2^(3*n/2+1/2) - (1+(-1)^n)*15/4*2^(3*n/2) + 6*2^n. - Vaclav Kotesovec, Nov 27 2012

Empirical g.f.: x*(1 - 3*x + 6*x^2 + 96*x^3 + 80*x^4 - 192*x^5) / ((1 - 2*x)*(1 - 4*x)*(1 - 8*x^2)). - Colin Barker, May 05 2018

EXAMPLE

Some solutions for 4 X 4:

  0        0        0        0        0        0        0        0

  0 1      1 2      1 1      1 2      1 2      1 2      1 2      0 1

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

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

CROSSREFS

Cf. A194893.

Sequence in context: A027324 A122741 A136325 * A103333 A037762 A037650

Adjacent sequences:  A194885 A194886 A194887 * A194889 A194890 A194891

KEYWORD

nonn

AUTHOR

R. H. Hardin, Sep 04 2011

STATUS

approved

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Last modified May 20 08:18 EDT 2022. Contains 353852 sequences. (Running on oeis4.)