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A125604 Minimum of the largest prime factors of a number and its two neighbors. 0
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 (list; graph; refs; listen; history; text; internal format)
OFFSET
3,1
LINKS
FORMULA
a(n)=min{lpf(n-1),lpf(n),lpf(n+1)}, where lpf is the largest prime factor: lpf(k)=A006530(n).
EXAMPLE
a(93) = min{lpf(92),lpf(93),lpf(94)} = min{23,31,47} = 23.
MATHEMATICA
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 *)
CROSSREFS
Cf. A093074.
Sequence in context: A262941 A127656 A109709 * A216685 A331853 A187184
KEYWORD
nonn
AUTHOR
Carlos Alves, Nov 27 2006
STATUS
approved

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Last modified March 28 05:39 EDT 2024. Contains 371235 sequences. (Running on oeis4.)