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A125604
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Minimum of the largest prime factors of a number and its two neighbors.
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0
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2, 2, 2, 3, 2, 2, 2, 3, 3, 3, 3, 5, 2, 2, 2, 3, 3, 5, 5, 7, 3, 3, 3, 3, 3, 3, 5, 5, 2, 2, 2, 7, 3, 3, 3, 13, 5, 5, 5, 7, 7, 5, 5, 5, 3, 3, 3, 5, 5, 13, 3, 3, 3, 7, 7, 19, 5, 5, 5, 7, 2, 2, 2, 11, 11, 17, 7, 7, 3, 3, 3, 5, 5, 5, 11, 11, 5, 3, 3, 3, 7, 7, 7, 17, 11, 11, 5, 5, 5, 13, 23, 19, 3, 3, 3, 7, 5, 5
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OFFSET
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3,1
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LINKS
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FORMULA
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a(n)=min{lpf(n-1),lpf(n),lpf(n+1)}, where lpf is the largest prime factor: lpf(k)=A006530(n).
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EXAMPLE
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a(93) = min{lpf(92),lpf(93),lpf(94)} = min{23,31,47} = 23.
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MATHEMATICA
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LPF = FactorInteger[ # ][[ -1, 1]] &; Map[Min[{LPF[ # - 1], LPF[ # ], LPF[ # + 1]}] &, Range[3, 200]]
Min/@Partition[Table[FactorInteger[n][[-1, 1]], {n, 110}], 3, 1] (* Harvey P. Dale, May 25 2015 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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