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%I #24 Sep 12 2020 10:32:32
%S 4,6,11,14,15,17,19,20,23,25,31,33,34,35,37,39,49,53,55,59,61,68,90,
%T 93,94,101,116,117,121,124,145,155,158,163,169,170,186,193,194,199,
%U 205,211,214,245,258,259,264,267,283,311,315,328,340,347,359,365,371,385
%N Numbers n such that the harmonic number numerator A001008(n) is a semiprime.
%C 414, 421, 425, 436, 451, 452, and 480 are in the sequence. 391 and 476 are the remaining candidates below 500. - _Daniel M. Jensen_, Jun 26 2020
%D R. L. Graham, D. E. Knuth and O. Patashnik, Concrete Mathematics. Addison-Wesley, Reading, MA, 1990, p. 259.
%D G. H. Hardy and E. M. Wright, An Introduction to the Theory of Numbers. 3rd ed., Oxford Univ. Press, 1954, page 347.
%D D. E. Knuth, The Art of Computer Programming. Addison-Wesley, Reading, MA, Vol. 1, p. 615
%H FactorDB, <a href="http://factordb.com/index.php?id=1100000000452032928">Status of Numerator(H_391) in factordb.com</a>
%H Hisanori Mishima, <a href="http://www.asahi-net.or.jp/~KC2H-MSM/mathland/matha1/matha126.htm">Wolstenholme number (n = 1 to 100</a>, <a href="http://www.asahi-net.or.jp/~KC2H-MSM/mathland/matha1/matha127.htm">n = 101 to 200</a>, <a href="http://www.asahi-net.or.jp/~KC2H-MSM/mathland/matha1/matha128.htm">n = 201 to 300</a>, <a href="http://www.asahi-net.or.jp/~KC2H-MSM/mathland/matha1/matha1281.htm">n = 301 to 400</a>, <a href="http://www.asahi-net.or.jp/~KC2H-MSM/mathland/matha1/matha1282.htm">n = 401 to 500</a>, <a href="http://www.asahi-net.or.jp/~KC2H-MSM/mathland/matha1/matha1283.htm">n = 501 to 600)</a>.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/WolstenholmesTheorem.html">Wolstenholme's Theorem</a>, <a href="http://mathworld.wolfram.com/HarmonicNumber.html">Harmonic Number</a>.
%Y Cf. A001008 (numerators of harmonic number H(n)=Sum_{i=1..n} 1/i).
%Y Cf. A002805, A056903, A067657.
%K hard,nonn
%O 1,1
%A _Alexander Adamchuk_, Dec 24 2008
%E More terms from _Sean A. Irvine_, Aug 22 2011
%E Two missing terms added by _D. S. McNeil_, Aug 23 2011
%E More terms from _Sean A. Irvine_, Apr 01 2013
%E Two more terms from _Daniel M. Jensen_, Jun 26 2020
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