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 A128648 Denominator of Sum[ (-1)^(k+1)*1/(Prime[k]-1), {k,1,n} ]. 3

%I

%S 1,2,4,12,60,5,80,720,7920,55440,55440,6160,6160,18480,425040,5525520,

%T 160240080,160240080,53413360,53413360,480720240,480720240,

%U 19709529840,19709529840,39419059680,197095298400,3350620072800,177582863858400

%N Denominator of Sum[ (-1)^(k+1)*1/(Prime[k]-1), {k,1,n} ].

%C A128647(n) = {1,1,3,7,41,3,53,437,5167,34189,36037,3833,3987,11521,...} = Numerator of Sum[ (-1)^(k+1)*1/(Prime[k]-1), {k,1,n} ]. A128646(n) = {1,2,4,12,60,10,80,720,7920,55440,55440,18480,18480,18480,425040,...} = Denominator of Sum[ 1/(Prime[k]-1), {k,1,n} ]. Numbers n such that a(n) equals A128646(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 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/PrimeSums.html">Prime Sums</a>

%F a(n) = Denominator[ Sum[ (-1)^(k+1)*1/(Prime[k]-1), {k,1,n} ] ].

%t Table[Denominator[Sum[(-1)^(k+1)*1/(Prime[k]-1),{k,1,n}]],{n,1,36}]

%Y Cf. A128647 = Numerator of Sum[ (-1)^(k+1)*1/(Prime[k]-1), {k, 1, n} ]. Cf. A128646 = Denominator of Sum[ 1/(Prime[k]-1), {k, 1, n} ]. Cf. A128649, A120271, A119686, A006093, A000040.

%K frac,nonn

%O 1,2

%A _Alexander Adamchuk_, Mar 18 2007

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Last modified August 7 11:07 EDT 2020. Contains 336275 sequences. (Running on oeis4.)