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8, 24, 72, 216, 648, 1944, 5832, 17496, 52488, 157464, 472392, 1417176, 4251528, 12754584, 38263752, 114791256, 344373768, 1033121304, 3099363912, 9298091736, 27894275208, 83682825624, 251048476872, 753145430616, 2259436291848, 6778308875544, 20334926626632
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OFFSET
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0,1
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COMMENTS
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For n>=3, a(n-3) is equal to the number of functions f:{1,2,...,n}->{1,2,3} such that for fixed, different x_1, x_2, x_3 in {1,2,...,n} and fixed y_1, y_2, y_3 in {1,2,3} we have f(x_i)<>y_i, (i=1,2,3). - Milan Janjic, May 13 2007
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LINKS
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FORMULA
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a(n) = 3*a(n-1). G.f.: 8/(1-3*x). - Colin Barker, Jul 02 2012
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MATHEMATICA
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PROG
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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