

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
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OFFSET

1,1


COMMENTS

This is the largest single divisor contributing to A136021(n).
If 4 concatenated with n1 nines is prime, it will be the largest factor. This candidate does not work for n=6 because 499999 is not prime.


LINKS

Robert Israel, Table of n, a(n) for n = 1..501


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

Cf. A136021, A052369.
Sequence in context: A241372 A124267 A124450 * A328032 A074192 A058806
Adjacent sequences: A136020 A136021 A136022 * A136024 A136025 A136026


KEYWORD

nonn


AUTHOR

Enoch Haga, Dec 12 2007


EXTENSIONS

Edited and more terms added by R. J. Mathar, Apr 17 2009


STATUS

approved



