A165318 - OEIS

%I #15 Apr 14 2019 01:42:05

%S 2,3,7,11,23,31,41,43,47,59,67,71,79,83,89,103,107,131,137,139,167,

%T 179,191,211,223,227,233,239,251,263,271,281,283,311,313,331,347,359,

%U 367,379,383,409,419,431,439,443,457,463,467,479,499,503,521,547,563,569

%N Primes p where the number of divisors of p-1 is a power of 2.

%H Harvey P. Dale, <a href="/A165318/b165318.txt">Table of n, a(n) for n = 1..1000</a>

%p isA000079 := proc(n) RETURN( n=1 or numtheory[factorset](n) = {2}) ; end: A165318 := proc(n) if n = 1 then 2; else p := nextprime(procname(n-1)) ; while not isA000079(numtheory[tau](p-1)) do p := nextprime(p) ; od; p ; fi; end: seq(A165318(n),n=1..90) ; # _R. J. Mathar_, Sep 18 2009

%t Select[Prime[Range[200]],IntegerQ[Log[2,DivisorSigma[0,#-1]]]&] (* _Harvey P. Dale_, Oct 14 2018 *)

%Y Cf. A165319, A165320.

%K nonn

%O 1,1

%A _Leroy Quet_, Sep 14 2009

%E More terms from _R. J. Mathar_, Sep 18 2009