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 A064404 When the numerator - denominator (A064169) in n-th harmonic number is prime. 1
 3, 4, 6, 7, 10, 19, 20, 26, 30, 31, 33, 40, 63, 85, 92, 100, 126, 131, 185, 196, 200, 204, 242, 246, 272, 274, 282, 379, 553, 572, 654, 777, 902, 1100, 1216, 1225, 1236, 1316, 1413, 1658, 1943, 2077, 2086, 2744, 2746, 2856, 2860, 3518, 3718, 4184, 4189, 4363 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Amiram Eldar, Table of n, a(n) for n = 1..92 Henri Lifchitz and Renaud Lifchitz, PRP Records MATHEMATICA s = 1; Do[ m = n; s = s + 1/n; If[ PrimeQ[ Numerator[ s ] - Denominator[ s ] ], Print[ n ] ], {n, 2, 2500} ] hnoQ[n_]:=Module[{h=HarmonicNumber[n]}, PrimeQ[Numerator[h]-Denominator[ h]]]; Select[Range[5000], hnoQ] (* Harvey P. Dale, May 23 2012 *) PROG (PARI) for(n=2, 300, if(isprime(lcm(n!, sum(k=2, n, 1/k))/n!), print1(n, ", "))); \\ Arkadiusz Wesolowski, Oct 13 2011 CROSSREFS Cf. A064169. Sequence in context: A024912 A108588 A194095 * A294488 A364341 A335059 Adjacent sequences: A064401 A064402 A064403 * A064405 A064406 A064407 KEYWORD nonn AUTHOR Robert G. Wilson v, Sep 28 2001 EXTENSIONS More terms from Arkadiusz Wesolowski, Oct 13 2011 STATUS approved

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Last modified August 15 13:43 EDT 2024. Contains 375173 sequences. (Running on oeis4.)