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A086258
a(n) is the smallest k such that 2^k+1 has n primitive prime factors.
1
0, 14, 26, 46, 83, 118, 309, 194, 414, 538, 786, 958
OFFSET
1,2
COMMENTS
A prime factor of 2^n+1 is called primitive if it does not divide 2^r+1 for any r<n. See A086257 for the number of primitive prime factors in 2^n+1. It is known that a(8) = 194.
Next term is > 666. - David Wasserman, Feb 25 2005
REFERENCES
J. Brillhart et al., Factorizations of b^n +- 1. Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002.
LINKS
J. Brillhart et al., Factorizations of b^n +- 1 Available on-line
EXAMPLE
a(2) = 14 because 2^14+1 = 5*29*113 and 29 and 113 do not divide 2^r+1 for r < 14.
CROSSREFS
Sequence in context: A242395 A112772 A155505 * A372008 A063799 A086451
KEYWORD
nonn,hard,more
AUTHOR
T. D. Noe, Jul 14 2003
EXTENSIONS
More terms from David Wasserman, Feb 25 2005
a(11) from D. S. McNeil, Dec 19 2010
a(12) from Amiram Eldar, Oct 12 2019
STATUS
approved