|
| |
|
|
A086252
|
|
a(n) is the smallest k such that 2^k-1 has n primitive prime factors.
|
|
2
| | |
|
|
|
OFFSET
| 1,1
|
|
|
COMMENTS
| A prime factor of 2^n-1 is called primitive if it does not divide 2^r-1 for any r<n. Equivalently, p is a primitive prime factor of 2^n-1 if ord(2,p)=n. See A086251 for the number of primitive prime factors in 2^n-1.
No more terms < 673. (2^673-1 is the first that is not completely factored in the linked reference.) - David Wasserman (wasserma(AT)spawar.navy.mil), Feb 22 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) = 11 because 2^11-1 = 23*89, both 23 and 89 have order 11 and the numbers 2^r-1 have only 0 or 1 primitive prime factors.
|
|
|
CROSSREFS
| Cf. A086251.
Sequence in context: A009312 A154251 A092275 * A106926 A133558 A140745
Adjacent sequences: A086249 A086250 A086251 * A086253 A086254 A086255
|
|
|
KEYWORD
| hard,more,nonn
|
|
|
AUTHOR
| T. D. Noe (noe(AT)sspectra.com), Jul 14 2003
|
|
|
EXTENSIONS
| More terms from David Wasserman (wasserma(AT)spawar.navy.mil), Feb 22 2005
|
| |
|
|
