%I A023272
%S A023272 2,5,89,179,359,509,1229,1409,2699,3539,6449,10589,11549,11909,12119,
%T A023272 17159,19709,19889,22349,26189,27479,30389,43649,53639,53849,55229,57839,
%U A023272 60149,61409,63419,66749,71399,74699,75329,82499,87539,98369,101399
%N A023272 Numbers n such that n remains prime through 3 iterations of function 
               f(x) = 2x + 1.
%t A023272 Select[Prime[Range[10^3*4]], PrimeQ[a1=2*#+1]&&PrimeQ[a2=2*a1+1]&&PrimeQ[a3=2*a2+1] 
               &] (from Vladimir Orlovsky (4vladimir(AT)gmail.com), May 01 2008)
%Y A023272 Cf. (A005384 and A005385), A007700, A023302, A023330, A057331, A005602.
%Y A023272 Sequence in context: A120798 A048187 A082431 this_sequence A057978 A093308 
               A162569
%Y A023272 Adjacent sequences: A023269 A023270 A023271 this_sequence A023273 A023274 
               A023275
%K A023272 nonn
%O A023272 1,1
%A A023272 David W. Wilson (davidwwilson(AT)comcast.net)