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A136023
The largest prime factor among all composites <= 10^n.
2
5, 47, 499, 4999, 49999, 499979, 4999999, 49999991, 499999993, 4999999937, 49999999967, 499999999979, 4999999999937, 49999999999981, 499999999999999, 4999999999999997, 49999999999999993, 499999999999999931, 4999999999999999963, 49999999999999999951
OFFSET
1,1
COMMENTS
This is the largest single divisor contributing to A136021(n).
If 4 concatenated with n-1 nines is prime, it will be the largest factor. This candidate does not work for n=6 because 499999 is not prime.
LINKS
EXAMPLE
a(3)=499 because it is the largest prime factor of all k<=10^3; the largest k in that interval with this factor is k=2*499 = 998.
MAPLE
5, seq(prevprime(5*10^n), n=1..100); # Robert Israel, Jul 21 2014
CROSSREFS
Sequence in context: A241372 A124267 A124450 * A370100 A328032 A074192
KEYWORD
nonn
AUTHOR
Enoch Haga, Dec 12 2007
EXTENSIONS
Edited and more terms added by R. J. Mathar, Apr 17 2009
STATUS
approved