login
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
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)).
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
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Sep 29 2002
EXTENSIONS
Corrected by Harvey P. Dale, Feb 18 2011
STATUS
approved