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A126196 Numbers n such that gcd(A001008(n),A001008([n/2])) > 1. 12
7, 546, 1092, 1755, 3510, 4896, 52447, 670668 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Note a connection to the Wieferich primes A001220: a(3) = A001220(1) - 1. a(4) = (A001220(2)-1)/2. a(5) = A001220(2) - 1.

a(9) > 840000. - Giovanni Resta, May 13 2016

LINKS

Table of n, a(n) for n=1..8.

MATHEMATICA

Select[Range[5000], GCD @@ Numerator@ HarmonicNumber@{#, Floor[#/2]} > 1 &] (* Giovanni Resta, May 13 2016 *)

PROG

(PARI) a001008(n)=numerator(sum(i=1, n, 1/i))

for(n=1, 1e6, if(gcd(a001008(n), a001008(n/2)) > 1, print1(n, ", "))) \\ Felix Fröhlich, Aug 08 2014

CROSSREFS

The corresponding GCDs are given by A126197.

Cf. A001008, A125581, A001220, A002805, A058313, A058312, A074791, A121594.

Sequence in context: A003396 A124899 A056852 * A182433 A093169 A159029

Adjacent sequences:  A126193 A126194 A126195 * A126197 A126198 A126199

KEYWORD

nonn,more

AUTHOR

Max Alekseyev and Tanya Khovanova, Mar 07 2007, corrected Mar 10 2007

EXTENSIONS

a(8) from Giovanni Resta, May 13 2016

STATUS

approved

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Last modified May 23 02:46 EDT 2017. Contains 286909 sequences.