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%I #13 Feb 22 2022 21:25:42
%S 11,23,101,167,199,347
%N Numbers k such that 2^k +- 1 are both semiprimes.
%C Intersection of A092559 and A085724.
%C a(7), if it exists, is at least 41519. - _Charles R Greathouse IV_, Jun 05 2013
%C 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
%e 11 is a term because 2^11 - 1 = 23*89 and 2^11 + 1 = 3*683.
%o (PARI) is(n)=isprime(n) && n>7 && ispseudoprime((2^n+1)/3) && bigomega(2^n-1)==2 \\ _Charles R Greathouse IV_, Jun 05 2013
%Y Subsequence of A000040.
%Y Cf. A092559, A085724, A092561, A092562.
%K nonn
%O 1,1
%A _Zak Seidov_, Feb 27 2004
%E a(6) from _Robert G. Wilson v_, Apr 18 2006
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