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A078559 Numerator of Product_{i=1..n} (p_i+1)/(p_i-1) where p_i is the i-th prime. 2
3, 6, 9, 12, 72, 84, 189, 21, 252, 270, 288, 304, 1596, 152, 3648, 49248, 295488, 1526688, 17302464, 622888704, 640191168, 1707176448, 10243058688, 23046882048, 23527025424, 599939148312, 47054050848, 2540918745792 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

REFERENCES

R. K. Guy, Unsolved Problems in Number Theory, B48.

LINKS

Robert Israel, Table of n, a(n) for n = 1..1701 (b-file corrected by Georg Fischer, Jan 16 2019)

F. Smarandache, Only Problems, Not Solutions!.

FORMULA

a(n) = A054640(n)/A078558(n).

MAPLE

Q:= 1: p:= 1:

for n from 1 to 100 do

  p:= nextprime(p);

  Q:= Q * (p+1)/(p-1);

  A[n]:= numer(Q);

od:

seq(A[i], i=1..100); # Robert Israel, May 11 2018

MATHEMATICA

Numerator[Table[Product[(Prime[i] + 1)/(Prime[i] - 1), {i, n}], {n, 30}]] (* Alonso del Arte, Aug 23 2011 *)

PROG

(PARI) a(n) = numerator(prod(i=1, n, (prime(i)+1)/(prime(i)-1))); \\ Michel Marcus, May 11 2018

CROSSREFS

Cf. A000203, A002110, A000005, A005867, A054640, A020492, A078558.

Denominators are in A078560.

Sequence in context: A072179 A065811 A061514 * A317557 A159908 A236761

Adjacent sequences:  A078556 A078557 A078558 * A078560 A078561 A078562

KEYWORD

nonn,frac

AUTHOR

Labos Elemer, Dec 06 2002

EXTENSIONS

Improved definition from Franklin T. Adams-Watters, Dec 02 2005

STATUS

approved

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Last modified February 20 11:01 EST 2020. Contains 332073 sequences. (Running on oeis4.)