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A055995
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a(n) = 64*9^(n-2), a(0)=1, a(1)=7.
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2
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1, 7, 64, 576, 5184, 46656, 419904, 3779136, 34012224, 306110016, 2754990144, 24794911296, 223154201664, 2008387814976, 18075490334784, 162679413013056, 1464114717117504, 13177032454057536, 118593292086517824
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OFFSET
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0,2
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COMMENTS
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For n>=2, a(n) is equal to the number of functions f:{1,2,...,n}->{1,2,3,4,5,6,7,8,9} such that for fixed, different x_1, x_2 in {1,2,...,n} and fixed y_1, y_2 in {1,2,3,4,5,6,7,8,9} we have f(x_1)<>y_1 and f(x_2)<> y_2. - Milan Janjic, Apr 19 2007
a(n) is the number of generalized compositions of n when there are 8*i-1 different types of i, (i=1,2,...). - Milan Janjic, Aug 26 2010
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REFERENCES
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A. H. Beiler, Recreations in the Theory of Numbers, Dover, N.Y., 1964, pp. 194-196.
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LINKS
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FORMULA
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a(n) = 9a(n-1) + ((-1)^n)*C(2, 2-n).
G.f.: (1-x)^2/(1-9x).
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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