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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(2) = (A001220(1) - 1)/2, a(3) = A001220(1) - 1, a(4) = (A001220(2) - 1)/2, a(5) = A001220(2) - 1. [Comment regarding a(2) added by Kevin J. Gomez, Jul 11 2017] a(9) > 840000. - Giovanni Resta, May 13 2016 LINKS 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 FrÃ¶hlich, Aug 08 2014 CROSSREFS The corresponding GCDs are given by A126197. Cf. A001008, A001220, A002805, A058312, A058313, A074791, A121594, A125581. Sequence in context: A056852 A316394 A300391 * A182433 A329368 A333208 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 September 21 12:13 EDT 2020. Contains 337271 sequences. (Running on oeis4.)