%I A125503
%S A125503 2,2,3,2,23,73,15,2,3,5,13,57,3,171,5,2,21,7,55,152,26
%N A125503 Smallest number k such that the numerator of generalized harmonic number 
               H(k,n) = Sum[ 1/i^n, {i,1,k} ] is a prime.
%C A125503 a(n) = 2 for n = {1,2,4,8,16,...}. Corresponding Fermat primes A019434 
               = {3, 5, 17, 257, 65537, ...}. a(n) = 3 for n = {3,9,13,25,27,29,
               95,107,153,159,...}. a(n) = 5 for n = {10,15,60,90,197,209,...}. 
               a(n) = 7 for n = {18,47,112,155,273,...}. a(n) = 15 for n = {7,30,
               43,...}. a(28) = 4. a(31) = 56. a(144) = 9.
%H A125503 Eric Weisstein's World of Mathematics, Link to a section of The World 
               of Mathematics. <a href="http://mathworld.wolfram.com/HarmonicNumber.html">
               Harmonic Number</a>.
%Y A125503 Cf. A001008, A007406, A007408, A007410, A099828.
%Y A125503 Cf. A019434.
%Y A125503 Sequence in context: A110088 A064998 A127012 this_sequence A127009 A164089 
               A068460
%Y A125503 Adjacent sequences: A125500 A125501 A125502 this_sequence A125504 A125505 
               A125506
%K A125503 hard,more,nonn
%O A125503 1,1
%A A125503 Alexander Adamchuk (alex(AT)kolmogorov.com), Dec 28 2006, Jan 31 2007