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Search: id:A028245
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| A028245 |
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5^(n-1) - 4*4^(n-1) + 6*3^(n-1) - 4*2^(n-1) + 1 (essentially Stirling numbers of second kind). |
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+0
1
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| 0, 0, 0, 0, 24, 360, 3360, 25200, 166824, 1020600, 5921520, 33105600, 180204024, 961800840, 5058406080, 26308573200, 135666039624, 694994293080, 3542142833040, 17980946172000, 90990301641624
(list; graph; listen)
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OFFSET
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1,5
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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}->{1,2,3,4,5} such that Im(f) contains 4 fixed elements. - Aleksandar M. Janjic and Milan R. Janjic (agnus(AT)blic.net), Mar 08 2007
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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)=24*S(n, 5)=24*A000481(n). - Emeric Deutsch (deutsch(AT)duke.poly.edu), May 02 2004
G.f.: -24*x^5/((x-1)*(4*x-1)*(3*x-1)*(2*x-1)*(5*x-1)) [From Maksym Voznyy (voznyy(AT)mail.ru), Jul 26 2009]
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CROSSREFS
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Cf. A000481, A008277.
Sequence in context: A075621 A137499 A122813 this_sequence A005546 A081144 A126780
Adjacent sequences: A028242 A028243 A028244 this_sequence A028246 A028247 A028248
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com), Doug McKenzie mckfam4(AT)aol.com
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EXTENSIONS
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G.f. proposed by Maksym Voznyy checked and corrected by R. J. Mathar, Sep 16 2009.
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