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reviewed
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editing
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Robert Israel, <a href="/A136023/b136023.txt">Table of n, a(n) for n = 1..501</a>
5, seq(prevprime(5*10^n), n=1..100); # Robert Israel, Jul 21 2014
approved
editing
_Enoch Haga (Enokh(AT)comcast.net), _, Dec 12 2007
Edited and more terms added by _R. J. Mathar (mathar(AT)strw.leidenuniv.nl), _, Apr 17 2009
Value of The largest prime factor under among all composites <= 10^n associated with A136021.
5, 47, 499, 4999, 49999, 499979, 4999999, 49999991, 499999993, 4999999937, 49999999967, 499999999979, 4999999999937, 49999999999981, 499999999999999, 4999999999999997, 49999999999999993, 499999999999999931, 4999999999999999963, 49999999999999999951
This is the largest single divisor contributing to A136021(n).
Whenever an even N occurs one factor is 2: if If 4 concatenated with n-1 nines is followed by any number of 9's, prime, it will be the largest factor if prime (. This candidate does not work for n=6 because 499999 is not prime).
Find the last instance of the largest prime factor under 10^n.
a(23)=499 because it is the largest prime factor of all N under k<=10^3; the value of N where largest k in that interval with this factor last occurs is k=2*499 = 998.
easy,more,nonn,uned,new
nonn
Edited and more terms added by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Apr 17 2009
Value of largest prime factor under 10^n associated with A136021.
5, 47, 499, 4999, 49999
1,1
Whenever an even N occurs one factor is 2: if 4 is followed by any number of 9's, it will be the largest factor if prime (499999 is not prime).
Find the last instance of the largest prime factor under 10^n.
a(2)=499 because it is the largest prime factor of all N under 10^3; the value of N where this factor last occurs is 2*499 = 998.
Cf. A136021.
easy,more,nonn,uned
Enoch Haga (Enokh(AT)comcast.net), Dec 12 2007
approved