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A057109 Numbers n that are not factors of P(n)!, where P(n) is the largest prime factor of n. 17

%I #50 Feb 25 2020 01:02:07

%S 4,8,9,12,16,18,24,25,27,32,36,45,48,49,50,54,64,72,75,80,81,90,96,98,

%T 100,108,121,125,128,135,144,147,150,160,162,169,175,180,189,192,196,

%U 200,216,224,225,240,242,243,245,250,256,270,288,289,294,300,320,324

%N Numbers n that are not factors of P(n)!, where P(n) is the largest prime factor of n.

%C These are also the numbers for which the Kempner function A002034 is composite. Their density approaches zero as they go to infinity. - _Jud McCranie_, Dec 08 2001

%C n is a member if and only if P(n) < A002034(n). The members are the exceptions to the rule that P(n) = A002034(n) for almost all n (Erdős and Kastanas 1994, Ivic 2004). - _Jonathan Sondow_, Jan 10 2005

%C Same as numbers n such that |e - m/n| < 1/(P(n)+1)! for some integer m. - _Jonathan Sondow_, Dec 29 2007

%D Steven R. Finch, Mathematical Constants, Cambridge, 2003, pp. 284-292.

%H Alois P. Heinz, <a href="/A057109/b057109.txt">Table of n, a(n) for n = 1..50000</a> (first 1750 terms from Vincenzo Librandi)

%H Paul Erdős and Ilias Kastanas, <a href="http://www.jstor.org/stable/2324376">Solution 6674: The smallest factorial that is a multiple of n</a>, Amer. Math. Monthly 101 (1994) 179.

%H Steven R. Finch, <a href="http://www.people.fas.harvard.edu/~sfinch/constant/golomb/smarand/smarand1.html">The Average Value of the Smarandache Function</a> [Broken link]

%H Steven R. Finch, <a href="http://fs.unm.edu/SF/TheAverageValue.pdf">The Average Value of the Smarandache Function</a>

%H Kevin Ford, <a href="https://faculty.math.illinois.edu/~ford/wwwpapers/nPn.pdf">On integers n for which n does not divide P(n)!</a>, University of Illinois at Urbana-Champaign (2019).

%H A. Ivic (2004), <a href="http://arXiv.org/abs/math/0311056">On a problem of Erdos involving the largest prime factor of n</a>, arXiv:math/0311056 [math.NT], 2003-2004.

%H C. Rivera, <a href="http://www.primepuzzles.net/conjectures/conj_027.htm">Conjecture about their density</a>

%H J. Sondow, <a href="http://www.jstor.org/stable/27642006">A geometric proof that e is irrational and a new measure of its irrationality</a>, Amer. Math. Monthly 113 (2006) 637-641.

%H J. Sondow, <a href="http://arXiv.org/abs/0704.1282">A geometric proof that e is irrational and a new measure of its irrationality</a>, arXiv:0704.1282 [math.HO], 2007-2010.

%H J. Sondow and E. W. Weisstein, <a href="http://mathworld.wolfram.com/SmarandacheFunction.html">MathWorld: Smarandache Function</a>

%e 12 is in the sequence since 3 is the largest prime factor of 12, but 12 is not a factor of 3! = 6.

%p with(numtheory): for n from 2 to 800 do if ifactors(n)[2][nops(ifactors(n)[2])][1]! mod n <> 0 then printf(`%d,`,n) fi; od:

%t Select[Range[330],Mod[FactorInteger[#][[-1,1]]!,#] != 0 &] (* _Jean-François Alcover_, May 19 2011 *)

%o (PARI) is(n)=my(s=factor(n)[, 1]); s[#s]!%n>0 \\ _Charles R Greathouse IV_, Sep 20 2012

%Y Subsequence of A122145.

%Y Cf. A002034, A006530, A057108.

%K easy,nonn

%O 1,1

%A _Henry Bottomley_, Aug 08 2000

%E More terms from _James A. Sellers_, Aug 22 2000

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Last modified March 28 22:04 EDT 2024. Contains 371254 sequences. (Running on oeis4.)