A128001 - OEIS

%I #16 May 09 2018 08:18:36

%S 2,3,7,27,51,55,81,1471,1483,8668,10885,20803,32605,36391,57004,61627,

%T 88651,89731

%N Numbers n such that (n-1)*2^n+1 is prime.

%t Select[Range[200], PrimeQ[(# - 1)*2^# + 1] &]  (* _G. C. Greubel_, May 08 2018 *)

%o (PARI) is(n)=ispseudoprime((n-1)<<n+1) \\ _Charles R Greathouse IV_, Jun 06 2017

%Y Cf. A029544, A002064.

%K nonn,more

%O 1,1

%A _N. J. A. Sloane_, Jan 25 2008

%E a(8)-a(14) from _Jason Earls_, Jan 29 2008

%E a(15)-a(18) from _Charles R Greathouse IV_, Oct 09 2011