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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.)