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A172461
Primes p such that 2*p-1 and 2^p-1 are both primes.
3
2, 3, 7, 19, 31, 607, 1279, 2281, 44497, 1257787, 13466917
OFFSET
1,1
EXAMPLE
a(1) = 2 is a term since it is a prime and 2^2 - 1 = 3 and 2*2 - 1 = 3 are primes.
a(2) = 3 is a term since it is a prime and 2^3 - 1 = 7 and 2*3 - 1 = 5 are primes.
MATHEMATICA
Select[MersennePrimeExponent[Range[47]], PrimeQ[2# -1] &] (* Amiram Eldar, Jul 29 2020 *)
CROSSREFS
Intersection of A000043 and A005382.
Cf. A000668.
Sequence in context: A152609 A298943 A340281 * A253971 A291339 A235616
KEYWORD
nonn,more
AUTHOR
Juri-Stepan Gerasimov, Feb 03 2010, Feb 06 2010
EXTENSIONS
a(9)-a(11) from Robert G. Wilson v, Feb 26 2010
STATUS
approved