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A001046
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a(n) = n(n-1)a(n-1)/2 + a(n-2).
(Formerly M1811 N0717)
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0
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1, 1, 2, 7, 44, 447, 6749, 142176, 3987677, 143698548, 6470422337, 356016927083, 23503587609815, 1833635850492653, 166884365982441238, 17524692064006822643, 2103129932046801158398, 286043195450428964364771
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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REFERENCES
| N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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EXAMPLE
| a(4) = 4*3*7/2 + 2 = 44.
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MATHEMATICA
| RecurrenceTable[{a[0]==a[1]==1, a[n]==n(n-1) a[n-1]/2+a[n-2]}, a[n], {n, 20}] (* From Harvey P. Dale, Sep 07 2011 *)
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CROSSREFS
| Cf. A001052.
Sequence in context: A196793 A128579 A194453 * A158257 A172389 A153522
Adjacent sequences: A001043 A001044 A001045 * A001047 A001048 A001049
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KEYWORD
| nonn,easy
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| More terms from James A. Sellers (sellersj(AT)math.psu.edu), Oct 05 2000
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