%I A086257
%S A086257 1,1,1,0,1,1,1,1,1,1,1,1,1,1,2,1,1,1,2,1,1,1,2,1,2,2,3,1,1,2,2,1,2,2,3,
%T A086257 2,2,2,3,1,1,2,2,1,2,1,4,2,2,1,3,3,2,2,2,2,2,2,2,3,1,1,4,1,2,3,2,2,2,2,
%U A086257 2,2,2,2,4,1,3,3,4,1,2,3,4,5,2,1,4,1,3,3,3,3,1,2,3,2,1,4,3,2,4,1,4,2,1
%N A086257 Number of primitive prime factors of 2^n+1.
%C A086257 A prime factor of 2^n+1 is called primitive if it does not divide 2^r+1 
               for any r<n. Zsigmondy's theorem says that there is at least one 
               primitive prime factor except for n=3. See A086258 for those n that 
               have a record number of primitive prime factors.
%H A086257 T. D. Noe, <a href="b086257.txt">Table of n, a(n) for n=0..500</a> (using 
               data from A001269)
%H A086257 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               ZsigmondyTheorem.html">Zsigmondy Theorem</a>
%e A086257 a(14) = 2 because 2^14+1 = 5*29*113 and 29 and 113 do not divide 2^r+1 
               for r < 14.
%t A086257 nMax=200; pLst={}; Table[f=Transpose[FactorInteger[2^n+1]][[1]]; f=Complement[f, 
               pLst]; cnt=Length[f]; pLst=Union[pLst, f]; cnt, {n, 0, nMax}]
%Y A086257 Cf. A046799 (number of distinct prime factors of 2^n+1), A054992 (number 
               of prime factors, with repetition, of 2^n+1), A086258.
%Y A086257 Sequence in context: A102097 A050330 A076398 this_sequence A161098 A136177 
               A066922
%Y A086257 Adjacent sequences: A086254 A086255 A086256 this_sequence A086258 A086259 
               A086260
%K A086257 hard,nonn
%O A086257 0,15
%A A086257 T. D. Noe (noe(AT)sspectra.com), Jul 14 2003