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A194888
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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.
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1
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1, 3, 24, 192, 1152, 5760, 26880, 118272, 506880, 2119680, 8761344, 35807232, 145539072, 588349440, 2372075520, 9538240512, 38303170560, 153613762560, 615659864064, 2465854390272, 9873068654592, 39518019256320, 158149336104960
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OFFSET
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1,2
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COMMENTS
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LINKS
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FORMULA
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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
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EXAMPLE
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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
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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