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.

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

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 A332451

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