A136683 - OEIS

A136683

Numbers k such that A136675(k) is prime.

2, 3, 4, 5, 6, 9, 20, 21, 29, 119, 132, 151, 351, 434, 457, 462, 572, 611, 930, 1107, 1157, 1452, 1515, 2838, 3997, 5346, 6463, 6725, 7664, 10234, 14168, 14299

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OFFSET

1,1

COMMENTS

A136675(k) = Numerator of Sum_{j=1..k} (-1)^(j+1)/j^3.

LINKS

Table of n, a(n) for n=1..32.

Eric Weisstein's World of Mathematics, Harmonic Number

MATHEMATICA

Do[ f=Numerator[ Sum[ (-1)^(k+1)*1/k^3, {k, 1, n} ] ]; If[ PrimeQ[f], Print[ {n, f} ] ], {n, 1, 151} ]

Flatten[Position[Numerator[Accumulate[Table[(-1)^(k+1) 1/k^3, {k, 3000}]]], _?PrimeQ] ] (* Harvey P. Dale, Feb 12 2013 *)

PROG

(PARI) isok(n) = ispseudoprime(numerator(sum(k=1, n, (-1)^(k+1) / k^3))); \\ Daniel Suteu, Mar 15 2019

CROSSREFS

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

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

Cf. A136681, A136682, A136684, A136685, A136686.

Sequence in context: A211676 A076299 A341015 * A200332 A303953 A195185

Adjacent sequences: A136680 A136681 A136682 * A136684 A136685 A136686

KEYWORD

nonn,more

AUTHOR

Alexander Adamchuk, Jan 16 2008

EXTENSIONS

More terms from Harvey P. Dale, Feb 12 2013

a(25)-a(28) from Amiram Eldar, Mar 15 2019

a(29)-a(32) from Robert Price, Apr 22 2019

STATUS

approved