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 A179871 #27 May 25 2025 09:23:30
%S A179871 1,2,5,10,11,17,22,23,29,34,41,46,47,53,55,58,59,71,82,83,85,89,91,94,
%T A179871 101,106,107,110,113,115,118,131,133,137,142,145,149,166,167,170,173,
%U A179871 178,179,182,187,191,197,202,205,214
%N A179871 Numbers h such that antiharmonic mean B(h) of the numbers k < h such that gcd(k, h) = 1 is an integer.
%C A179871 Numbers h such that B(h) = A053818(h) / A023896(h) = A175505(h) / A175506(h) is an integer.
%C A179871 Numbers h such that A175506(h) = 1.
%C A179871 Complement of A179872.
%C A179871 See A179873 (odd positive integers) for corresponding values A175505(a(n)).
%C A179871 Union of A003627 (primes of form 3n-1) and A179887.
%H A179871 Amiram Eldar, <a href="/A179871/b179871.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..2500 from Ivan Neretin)
%e A179871 a(9) = 29 because B(29) = A053818(29) / A023896(29) = 7714/406 = 19 (integer).
%t A179871 B[n_] := Plus @@ ((ks = Select[Range[n], GCD[n, #] == 1 &])^2)/Plus @@ ks; Select[Range[215], IntegerQ[B[#]] &] (* _Ivan Neretin_, May 22 2015 *)
%o A179871 (PARI) isok(k) = {my(f = factor(k)); if(k == 1, 1, denominator(2*k/3 + (1/3) * prod(i = 1, #f~, 1 - f[i, 1])/eulerphi(f)) == 1);} \\ _Amiram Eldar_, May 24 2025
%Y A179871 Cf. A179872, A179873, A179874, A179875, A179876, A179877, A179878, A179879, A179880, A179882, A179883, A179884, A179885, A179886, A179887, A179890, A179891.
%K A179871 nonn
%O A179871 1,2
%A A179871 _Jaroslav Krizek_, Jul 30 2010, Jul 31 2010