A092558 Numbers k such that 2^k +- 1 are both semiprimes.

11, 23, 101, 167, 199, 347

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

2^41519 + 1 is the product of 3 and a composite number, so if a(7) exists, it exceeds 41519. - Jon E. Schoenfield, Feb 22 2022

Links

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

Example

11 is a term 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