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A124879 Numbers k such that A027612(k) is prime. 4
2, 3, 6, 9, 18, 25, 29, 30, 39, 84, 91, 125, 130, 184, 195, 199, 203, 241, 245, 273, 281, 378, 552, 571, 653, 776, 901, 1099, 1215, 1224, 1235, 1315, 1412, 1657, 1942, 2076, 2085, 2743, 2745, 2855, 2859, 3517, 3717, 4183, 4188, 4362, 4547, 4728, 4783 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
Eric Weisstein's World of Mathematics, Harmonic Number.
EXAMPLE
A027612 begins {1, 5, 13, 77, 87, 223, 481, 4609, 4861, ...}.
Thus a(1) = 2, a(2) = 3, a(3) = 6, a(4) = 9.
MATHEMATICA
s=1; Do[s=s+1/(n+1); f=Numerator[(n+1)*(s-1)]; If[PrimeQ[f], Print[{n, f}]], {n, 1, 1942}]
PROG
(PARI) isok(n) = isprime(numerator(sum(k=1, n, k/(n-k+1)))); \\ Michel Marcus, Jul 14 2018
CROSSREFS
A027612(n) are the numerators of second order harmonic numbers H(n, (2)).
Corresponding primes in A027612 are listed in A124878.
Sequence in context: A351255 A018402 A018441 * A261661 A062865 A351018
KEYWORD
nonn
AUTHOR
Alexander Adamchuk, Nov 11 2006
EXTENSIONS
More terms from Stefan Steinerberger, May 29 2007
Crossrefs edited by Michel Marcus, Jul 14 2018
STATUS
approved

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Last modified March 28 14:38 EDT 2024. Contains 371254 sequences. (Running on oeis4.)