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A074767 Least m>n with spf(m)=gpf(n), where gpf(n) is the greatest prime factor of n and spf(m) is the smallest prime factor of m. 0
4, 9, 6, 25, 9, 49, 10, 15, 25, 121, 15, 169, 49, 25, 18, 289, 21, 361, 25, 49, 121, 529, 27, 35, 169, 33, 49, 841, 35, 961, 34, 121, 289, 49, 39, 1369, 361, 169, 55, 1681, 49, 1849, 121, 55, 529, 2209, 51, 77, 55, 289, 169, 2809, 57, 121, 77, 361, 841, 3481, 65 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(n)=gpf(n)^2 for n<gpf(n)^2; and for sqrt(n)-smooth numbers: a(n) <= gpf(n)*(least prime > n/gpf(n)).

LINKS

Table of n, a(n) for n=1..59.

MATHEMATICA

mfs={#, First[FactorInteger[#]][[1]]}&/@Range[3500];

Table[Select[Select[mfs, #[[2]]==Last[FactorInteger[n]][[1]]&], #[[1]]>n&][[1, 1]], {n, 2, 60}]  (* Harvey P. Dale, Feb 18 2011 *)

CROSSREFS

Cf. A006530, A020639, A064052, A048098, A007918.

Sequence in context: A140694 A152454 A287932 * A016097 A083717 A130041

Adjacent sequences:  A074764 A074765 A074766 * A074768 A074769 A074770

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Sep 29 2002

EXTENSIONS

Corrected by Harvey P. Dale, Feb 18 2011

STATUS

approved

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Last modified March 21 07:23 EDT 2019. Contains 321367 sequences. (Running on oeis4.)