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Search: id:A028244
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| A028244 |
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4^(n-1) - 3*3^(n-1) + 3*2^(n-1) - 1 (essentially Stirling numbers of second kind). |
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+0
2
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| 0, 0, 0, 6, 60, 390, 2100, 10206, 46620, 204630, 874500, 3669006, 15195180, 62350470, 254135700, 1030793406, 4166023740, 16792841910, 67558001700, 271392695406, 1089054420300, 4366671742950, 17498055448500, 70086339807006
(list; graph; listen)
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OFFSET
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1,4
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COMMENT
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For n>=4, a(n) is equal to the number of functions f: {1,2,...,n-1}->{1,2,3,4} such that Im(f) contains 3 fixed elements. - Aleksandar M. Janjic and Milan R. Janjic (agnus(AT)blic.net), Feb 27 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)=6*S(n, 4) = 6*A000453(n). - Emeric Deutsch (deutsch(AT)duke.poly.edu), May 02 2004
G.f.: 6x^4/((1-x)(1-2x)(1-3x)(1-4x)). [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Oct 23 2008]
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MATHEMATICA
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Table[4^(n - 1) - 3*3^(n - 1) + 3*2^(n - 1) - 1, {n, 1, 30}] - Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Apr 13 2006
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CROSSREFS
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Cf. A000453, A008277.
Sequence in context: A074441 A006741 A120573 this_sequence A000911 A076100 A043033
Adjacent sequences: A028241 A028242 A028243 this_sequence A028245 A028246 A028247
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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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