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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A128465 Numbers n such that n divides the numerator of alternating Harmonic number H'((n+1)/2) = A058313((n+1)/2). 1
 1, 5, 7, 71, 379, 2659 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For n>1 all 5 listed terms are primes. Numbers n such that n divides the numerator of alternating Harmonic number H'((n-1)/2) = A058313((n-1)/2) are listed in A128464(n) = {1073, 3511, ...}. Both known terms of A128464(n) are the Wieferich primes A001220(n) = {1093, 3511, ...} Primes p such that p^2 divides 2^(p-1) - 1. LINKS Eric Weisstein's World of Mathematics, Harmonic Number MATHEMATICA f=0; Do[ f = f + (-1)^(n+1)*1/n; g = Numerator[f]; If[ IntegerQ[ g/(2n-1) ], Print[2n-1]], {n, 1, 3000} ] CROSSREFS Cf. A001008 = Wolstenholme numbers: numerator of harmonic number H(n)=Sum_{i=1..n} 1/i. Cf. A058313 = Numerator of the n-th alternating harmonic number H'(n). Cf. A001220 = Wieferich primes p: p^2 divides 2^(p-1) - 1. Cf. A128463, A128464, A125854, A121999. Sequence in context: A308397 A308848 A109715 * A098967 A107140 A141746 Adjacent sequences:  A128462 A128463 A128464 * A128466 A128467 A128468 KEYWORD hard,more,nonn AUTHOR Alexander Adamchuk, Mar 10 2007 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.

Last modified April 23 00:56 EDT 2021. Contains 343197 sequences. (Running on oeis4.)