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A128648 Denominator of Sum[ (-1)^(k+1)*1/(Prime[k]-1), {k,1,n} ]. 3
1, 2, 4, 12, 60, 5, 80, 720, 7920, 55440, 55440, 6160, 6160, 18480, 425040, 5525520, 160240080, 160240080, 53413360, 53413360, 480720240, 480720240, 19709529840, 19709529840, 39419059680, 197095298400, 3350620072800, 177582863858400 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

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,...}.

LINKS

Table of n, a(n) for n=1..28.

Eric Weisstein's World of Mathematics, Prime Sums

FORMULA

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

MATHEMATICA

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

CROSSREFS

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.

Sequence in context: A000568 A177921 A301481 * A128646 A155747 A058254

Adjacent sequences:  A128645 A128646 A128647 * A128649 A128650 A128651

KEYWORD

frac,nonn

AUTHOR

Alexander Adamchuk, Mar 18 2007

STATUS

approved

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Last modified April 20 22:22 EDT 2019. Contains 322310 sequences. (Running on oeis4.)