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Search: id:A055842
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| A055842 |
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A second order recursive sequence. |
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+0
1
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| 1, 3, 16, 80, 400, 2000, 10000, 50000, 250000, 1250000, 6250000, 31250000, 156250000, 781250000, 3906250000, 19531250000, 97656250000, 488281250000, 2441406250000
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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First differences of A005054.
For n>=2, a(n) is equal to the number of functions f:{1,2,...,n}->{1,2,3,4,5} 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} we have f(x_1)<>y_1 and f(x_2)<> y_2. - Milan R. Janjic (agnus(AT)blic.net), Apr 19 2007
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REFERENCES
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A. H. Beiler, Recreations in the Theory of Numbers, Dover, N.Y., 1964, pps. 194-196.
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LINKS
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Milan Janjic, Enumerative Formulas for Some Functions on Finite Sets
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FORMULA
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a(n)=16*5^(n-2), a(0)=1, a(1)=3.
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EXAMPLE
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a(n)=5a(n-1)+[(-1)^n]*C(2,2-n). G.f.(x)=(1-x)^2/(1-5x).
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CROSSREFS
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Cf. A000351 and A005054.
Sequence in context: A003769 A005386 A053572 this_sequence A037773 A037661 A072615
Adjacent sequences: A055839 A055840 A055841 this_sequence A055843 A055844 A055845
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KEYWORD
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easy,nonn
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AUTHOR
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Barry E. Williams, May 30 2000
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