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A125839
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a(n) is the smallest number m such that k*m - 1 is prime for all k=3,4,...,n.
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4
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1, 1, 6, 18, 120, 1260, 1485540, 28667100, 28667100, 842889105240, 2281585556250, 163881570370980, 45187548280664790
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OFFSET
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3,3
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COMMENTS
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For n > 6, 10 divides a(n).
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LINKS
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EXAMPLE
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a(11)=28667100 because 3*28667100-1, 4*28667100-1, 5*28667100-1, 6*28667100-1, 7*28667100-1, 8*28667100-1, 9*28667100-1, 10*28667100-1 & 11*28667100-1 are prime and 28667100 is the smallest number with this property.
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MATHEMATICA
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a[n_] := Block[{k = If[n<5, 1, 6], s}, s = k; While[! AllTrue[k Range[3, n] - 1, PrimeQ], k += s]; k]; a /@ Range[3, 9] (* Giovanni Resta, Mar 29 2017 *)
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CROSSREFS
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KEYWORD
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hard,more,nonn
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AUTHOR
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Luke Pebody (luke.pebody(AT)gmail.com), Jan 02 2007
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EXTENSIONS
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STATUS
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approved
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