A136681 Numbers k such that A058313(k) is prime.

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

Author

Alexander Adamchuk, Jan 16 2008

Keywords

• nonn

Comments

A058313(k) = Numerator of Sum_{j=1..k} (-1)^(j+1)/j.

Links

• Eric Weisstein's World of Mathematics, Harmonic Number

Crossrefs

Cf. A058313, A119682, A120296, A136675, A136676, A136677.

Cf. A001008, A007406, A007408, A007410, A099828, A103345.

Cf. A136682, A136683, A136684, A136685, A136686.

Programs

Mathematica

Do[ f=Numerator[ Sum[ (-1)^(k+1)*1/k, {k,1,n} ] ]; If[ PrimeQ[f], Print[ {n,f} ] ], {n,1,317} ]

PARI

isok(n) = isprime(numerator(sum(k=1, n, (-1)^(k+1)/k))); \\ Michel Marcus, Mar 14 2019

Extensions

a(25)-a(30) from James R. Buddenhagen, Sep 22 2015

a(31)-a(51) from Amiram Eldar, Mar 14 2019