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A063684 Numbers k such that m(k!) = 2, where m(k) = mu(k) + mu(k+1) + mu(k+2). 0
8, 13, 14, 18, 19, 20, 25, 36, 38, 43, 48, 51, 52, 54, 60, 71, 74, 75, 78, 80, 87, 91, 92, 105, 108, 110, 112, 114 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Equivalently, k such that m(k!) = 2, where m(k) = mu(k+1) + mu(k+2), as mu(k!)=0 for all k >= 4 (because 4=2^2 divides k!). - Rick L. Shepherd, Aug 20 2003
127 belongs to the sequence. - Serge Batalov, Feb 17 2011
LINKS
Paul Leyland, Factors of n!+1 (updated 1 Oct 2006).
EXAMPLE
8 is a term: 8! = 40320; mu(40320) = 0, mu(40321) = 1, mu(40322) = 1, 0+1+1 = 2.
98 is not a term because 98! + 2 = 2 * 31003012014959 * 114951592532951 * 2015644865638913835753087050212028452990938458387 * P78 has an odd number of factors. - Sean A. Irvine, Feb 03 2010
PROG
(PARI) m(n) = moebius(n)+moebius(n+1)+moebius(n+2); for(n=1, 10^4, if(m(n!)==2, print(n)))
CROSSREFS
Cf. A084846 (mu(n!+1)).
Sequence in context: A124159 A128662 A133192 * A059194 A253775 A168137
KEYWORD
more,nonn
AUTHOR
Jason Earls, Aug 22 2001
EXTENSIONS
More terms from Rick L. Shepherd, Aug 20 2003
Two more terms from Sean A. Irvine, Feb 03 2010, Feb 08 2010
Two new terms, 105 and 108, from Daniel M. Jensen, Feb 19 2011, Mar 02 2011
Two more terms, 110 and 112, from Serge Batalov, Mar 04-05 2011
One more term, 114, from Sean A. Irvine, May 25 2015
STATUS
approved

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Last modified April 14 13:17 EDT 2024. Contains 371661 sequences. (Running on oeis4.)