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A092558 Numbers n such that 2^n +/- 1 are both semiprimes. 6
11, 23, 101, 167, 199, 347 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Intersection of A092559 and A085724.

a(7), if it exists, is at least 41519. - Charles R Greathouse IV, Jun 05 2013

LINKS

Table of n, a(n) for n=1..6.

EXAMPLE

11 is a member because 2^11-1=23*89 and 2^11+1=3*683.

PROG

(PARI) is(n)=isprime(n) && n>7 && ispseudoprime((2^n+1)/3) && bigomega(2^n-1)==2 \\ Charles R Greathouse IV, Jun 05 2013

CROSSREFS

Subsequence of A000040.

Cf. A092559, A085724, A092561, A092562.

Sequence in context: A077707 A081981 A081982 * A294255 A088777 A041238

Adjacent sequences:  A092555 A092556 A092557 * A092559 A092560 A092561

KEYWORD

nonn

AUTHOR

Zak Seidov, Feb 27 2004

EXTENSIONS

a(6) from Robert G. Wilson v, Apr 18 2006

STATUS

approved

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Last modified February 23 16:15 EST 2020. Contains 332174 sequences. (Running on oeis4.)