login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A320076 a(n) is smallest positive integer i such that difference of numerator and denominator of sum of j^(-i), when j=1..n and n > 2, is prime. 1
1, 1, 2, 1, 1, 2, 32, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

3,3

COMMENTS

a(11) > 6360.

a(11) > 12000. - Chai Wah Wu, Nov 15 2018

a(19) = a(20) = a(26) = a(30) = a(31) = a(33) = a(40) = 1, a(44) = a(48) = a(49) = 2, a(42) = 3, a(14) = 5, a(24) = a(46) = 7, a(12) = 8, a(13) = 17, a(47) = 19, a(25) = 49, a(38) = 54, a(37) = 179, a(16) = 207, a(22) = 676, a(18) = 690, a(43) = 880, a(17) = 1068, a(34) = 1199. - Chai Wah Wu, Nov 20 2018

a(15) = 2590, a(23) = 3734. - Chai Wah Wu, Nov 21 2018

LINKS

Table of n, a(n) for n=3..10.

MATHEMATICA

a[n_] := Do[s = HarmonicNumber[n, r]; If[PrimeQ[Numerator[s] - Denominator[s]], Return[r]], {r, 1, Infinity}]; Table[a[n], {n, 3, 10}] (* Vaclav Kotesovec, Nov 14 2018 *)

PROG

(PARI)

a(n)={for(i=1, +oo, s=sum(j=1, n, j^(-i)); p=numerator(s); q=denominator(s); if(ispseudoprime(p-q), return(i)))};

CROSSREFS

Cf. A320077.

Sequence in context: A028306 A111259 A304195 * A138948 A186114 A326934

Adjacent sequences:  A320073 A320074 A320075 * A320077 A320078 A320079

KEYWORD

nonn,more

AUTHOR

Dmitry Ezhov, Oct 05 2018

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified September 23 01:32 EDT 2020. Contains 337291 sequences. (Running on oeis4.)