%I A128646
%S A128646 1,2,4,12,60,10,80,720,7920,55440,55440,18480,18480,18480,425040,
%T A128646 5525520,160240080,53413360,160240080,160240080,480720240,480720240,
%U A128646 19709529840,19709529840,39419059680,197095298400,3350620072800
%N A128646 Denominator of Sum[ 1/(Prime[k]-1), {k,1,n} ].
%C A128646 A120271(n) = {1,3,7,23,121,21,173,1597,17927,127469,129317,...} = Numerator 
               of Sum[ 1/(Prime[k]-1), {k,1,n} ]. A128648(n) = {1,2,4,12,60,5,80,
               720,7920,55440,55440,6160,6160,18480,...} = Denominator of Sum[ (-1)^(k+1)*1/
               (Prime[k]-1), {k,1,n} ]. Numbers n such that a(n) equals A128648(n) 
               are listed in A128649(n) = {1,2,3,4,5,7,8,9,10,11,14,15,16,17,21,
               22,23,24,25,26,27,28,29,30,31,32,33,34,35,65,66,71,...}.
%H A128646 Eric Weisstein, Link to a section of The World of Mathematics. <a href="http:/
               /mathworld.wolfram.com/PrimeSums.html">Prime Sums</a>.
%F A128646 a(n) = Denominator[ Sum[ 1/(Prime[k]-1), {k,1,n} ] ].
%t A128646 Table[Denominator[Sum[1/(Prime[k]-1),{k,1,n}]],{n,1,36}]
%Y A128646 Cf. A120271 = Numerator of Sum[ 1/(Prime[k]-1), {k, 1, n} ]. Cf. A128649, 
               A128647, A128648 = Denominator of Sum[ (-1)^(k+1)*1/(Prime[k]-1), 
               {k, 1, n} ]. Cf. A119686, A006093, A000040.
%Y A128646 Sequence in context: A099928 A000568 A128648 this_sequence A155747 A058254 
               A076244
%Y A128646 Adjacent sequences: A128643 A128644 A128645 this_sequence A128647 A128648 
               A128649
%K A128646 frac,nonn
%O A128646 1,2
%A A128646 Alexander Adamchuk (alex(AT)kolmogorov.com), Mar 18 2007