This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A250095 #19 Mar 02 2020 08:54:02 %S A250095 4,27,28,54,56,64,68,91,99,100,133,138,148,154,165,188,217,222,247, %T A250095 259,268,276,279,290,301,308,369,375,388,403,414,427,428,430,469,474, %U A250095 481,508,511,540,544,548,549,553,559,589,609,621,627,628,639,642,665,668 %N A250095 Positive integers k such that the numerator of the harmonic mean of the proper divisors of k is equal to k. %H A250095 Amiram Eldar, <a href="/A250095/b250095.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..2000 from Colin Barker) %e A250095 27 is a term because the proper divisors of 27 are [1,3,9] and 3 / (1/1 + 1/3 + 1/9) = 27/13. %t A250095 Select[Range[668], CompositeQ[#] && Numerator[(DivisorSigma[0, #] - 1) * #/(DivisorSigma[1, #] - 1)] == # &] (* _Amiram Eldar_, Mar 02 2020 *) %o A250095 (PARI) %o A250095 harmonicmean(v) = #v / sum(k=1, #v, 1/v[k]) %o A250095 properdivisors(n) = d=divisors(n); vector(#d-1, k, d[k]) %o A250095 s=[]; for(n=2, 1000, if(numerator(harmonicmean(properdivisors(n)))==n, s=concat(s, n))); s %Y A250095 Cf. A247081, A250094. %K A250095 nonn %O A250095 1,1 %A A250095 _Colin Barker_, Nov 12 2014