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Search: id:A055846
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| A055846 |
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A second order recursive sequence. |
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+0
1
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| 1, 4, 25, 150, 900, 5400, 32400, 194400, 1166400, 6998400, 41990400, 251942400, 1511654400, 9069926400, 54419558400, 326517350400, 1959104102400, 11754624614400, 70527747686400, 423166486118400, 2538998916710400
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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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} 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} 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)=25*6^(n-2), a(0)=1, a(1)=4. a(n)=6a(n-1)+[(-1)^n]*binomial(2, 2-n); G.f.(x)=(1-x)^2/(1-6x).
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CROSSREFS
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First differences of A052934. Cf. A000400.
Sequence in context: A015533 A079291 A072221 this_sequence A091634 A010909 A079750
Adjacent sequences: A055843 A055844 A055845 this_sequence A055847 A055848 A055849
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KEYWORD
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easy,nonn
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AUTHOR
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Barry E. Williams, Jun 03 2000
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EXTENSIONS
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More terms from James A. Sellers (sellersj(AT)math.psu.edu), Jun 05 2000
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