%I A085917
%S A085917 5,4,2,1,3,5,4,2,1,2,1,3,6,3,3,3,3,6,3,3,3,2,1,3,6,3,6,3,6,3,3,11,16,8,
%T A085917 4,2,1,8,4,2,1,15,13,15,16,8,4,2,1,6,3,17,15,12,6,3,4,2,1,3,6,3,3,5,3,
               2,
%U A085917 1,5,6,3,48,24,12,6,3,12,6,3,10,5,4,2,1,3,3,31,21,17,15,11,13,24,12,6,
               3
%N A085917 Least k such that k*2^n - 1 is a semiprime.
%C A085917 The first few values of n such that 509203*2^n - 1 is a semiprime, where 
               k = 509203 (the conjectured smallest Riesel number), are: 3,4,16,
               34,61,82,124,142,163,171,... Conjecture: there are infinitely many 
               semiprimes of this form.
%e A085917 a(33)=16 because k*2^33 - 1 is not a semiprime for k=1,2,...15, but 16*2^33 
               - 1 = 223 * 616318177 is.
%Y A085917 Cf. A001358, A085427, A076337, A085245.
%Y A085917 Sequence in context: A108440 A102220 A109430 this_sequence A102593 A090462 
               A081749
%Y A085917 Adjacent sequences: A085914 A085915 A085916 this_sequence A085918 A085919 
               A085920
%K A085917 nonn
%O A085917 1,1
%A A085917 Jason Earls (zevi_35711(AT)yahoo.com), Aug 16 2003