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%I #29 Nov 21 2013 12:50:20
%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[9000]],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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