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 A196303 Numbers n such that both n and (n-1)*2^n+1 are primes. 0

%I

%S 2,3,7,1471,1483,61627,88731

%N Numbers n such that both n and (n-1)*2^n+1 are primes.

%C Primes p such that (p-1)*2^p+1 is also prime.

%e a(1)=2 because 2 and (2-1)*2^2+1=5 are both prime.

%e a(2)=3 because 3 and (3-1)*2^3+1=17 are both prime.

%e a(3)=7 because 7 and (7-1)*2^7+1=769 are both prime.

%t Select[Prime[Range],PrimeQ[(#-1)2^#+1]&] (* _Harvey P. Dale_, Jan 19 2012 *)

%o (PARI) forprime(n=1,1e4,if(ispseudoprime((n-1)<<n+1),print1(n", "))) \\ _Charles R Greathouse IV_, Oct 09 2011

%Y Subsequence of A128001.

%Y Cf. A029544, A196421, A196446.

%K nonn

%O 1,1

%A _Juri-Stepan Gerasimov_, Oct 02 2011

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Last modified July 10 16:22 EDT 2020. Contains 335577 sequences. (Running on oeis4.)