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A136681
Numbers k such that A058313(k) is prime.
8
3, 4, 5, 6, 9, 10, 13, 16, 17, 18, 37, 43, 58, 121, 124, 126, 137, 203, 247, 283, 285, 286, 289, 317, 424, 508, 751, 790, 937, 958, 1066, 1097, 1151, 1166, 1194, 1199, 1235, 1414, 1418, 1460, 1498, 1573, 2090, 2122, 2691, 2718, 3030, 3426, 3600, 3653, 3737
OFFSET
1,1
COMMENTS
A058313(k) = Numerator of Sum_{j=1..k} (-1)^(j+1)/j.
LINKS
Eric Weisstein's World of Mathematics, Harmonic Number
MATHEMATICA
Do[ f=Numerator[ Sum[ (-1)^(k+1)*1/k, {k, 1, n} ] ]; If[ PrimeQ[f], Print[ {n, f} ] ], {n, 1, 317} ]
PROG
(PARI) isok(n) = isprime(numerator(sum(k=1, n, (-1)^(k+1)/k))); \\ Michel Marcus, Mar 14 2019
KEYWORD
nonn
AUTHOR
Alexander Adamchuk, Jan 16 2008
EXTENSIONS
a(25)-a(30) from James R. Buddenhagen, Sep 22 2015
a(31)-a(51) from Amiram Eldar, Mar 14 2019
STATUS
approved