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%I A337935 #10 Oct 05 2020 05:08:19
%S A337935 2,3,4,5,7,8,9,11,13,16,17,19,23,25,27,29,31,32,37,41,43,47,49,53,59,
%T A337935 61,64,67,71,73,79,81,83,89,97,101,103,107,109,113,121,125,127,128,
%U A337935 131,137,139,149,151,157,163,167,169,173,179,181,190,191,193,197,199,211,223,227,229,233,239,241
%N A337935 Numbers with integer contraharmonic mean of distinct prime factors.
%C A337935 Similar sequences are A078174 (with respect to arithmetic mean) and A246655 (with respect to geometric mean).
%C A337935 Up to 10^6 there are 2637 terms that are not in A000961 (and in A246655). The list starts: 190, 380, 390, 615, 638, 710, 760, 780, 950, 1170, 1235, 1276, 1365, 1420, 1518, 1520, 1558, 1560, 1770, 1845, 1900, 1950, 2340, 2552, 2840, ...
%H A337935 Wikipedia, <a href="https://en.wikipedia.org/wiki/Contraharmonic_mean">Contraharmonic mean</a>
%e A337935 The distinct prime factors of 190 are {2,5,19} and their contraharmonic mean is (4+25+361)/(2+5+19) = 15. Therefore, 190 is a term.
%t A337935 pf[n_]:=First/@FactorInteger[n];
%t A337935 Select[Range[2,241],IntegerQ[ContraharmonicMean[pf[#]]]&]
%o A337935 (PARI) isok(m) = if (m>1, my(f=factor(m)); !(norml2(f[,1]) % vecsum(f[,1]))); \\ _Michel Marcus_, Oct 01 2020
%Y A337935 Cf. A078174, A246655 (subsequence).
%K A337935 nonn
%O A337935 1,1
%A A337935 _Ivan N. Ianakiev_, Oct 01 2020

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