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

1,1

Comments

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

Links

Table of n, a(n) for n=1..51.

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

Crossrefs

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

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

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

Sequence in context: A050414 A342469 A266322 * A206330 A104373 A047427

Adjacent sequences: A136678 A136679 A136680 * A136682 A136683 A136684

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