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 A102408 #17 Oct 19 2024 08:34:54
%S A102408 1,5,6,8,9,11,10,15,15,14,17,24,24,21,13,19,27,25,29,26,44,44,29,46,
%T A102408 39,46,27,42,47,47,54,35,41,60,51,37,48,45,49,50,49,53,77,86,86,51,96,
%U A102408 75,70,80,99,110,81,84,102,82,96,114,53,108,115,105,116,91
%N A102408 Harmonic means associated with A090945.
%C A102408 A perfect number N = 2^(p-1)*M(p) (A000396), with associated Mersenne prime M(p) = 2^p -1 (A000668), has harmonic mean N*tau(N)/sigma(N) = p (A000043).
%H A102408 Amiram Eldar, <a href="/A102408/b102408.txt">Table of n, a(n) for n = 1..930</a>
%F A102408 a(n) = m*tau(m)/sigma(m), where m = A090945(n), tau = A000005 and sigma = A000203.
%o A102408 (PARI) lista(nn) = {for (n=1, nn, ab = sigma(n)/n; hm = numdiv(n)/ab; if ((type(hm) == "t_INT") && (ab != 2), print1(hm, ", ")););} \\ _Michel Marcus_, Oct 26 2013
%Y A102408 Cf. A000005, A000043, A000203, A000396, A000668, A090945.
%K A102408 nonn
%O A102408 1,2
%A A102408 _Lekraj Beedassy_, Jan 07 2005
%E A102408 a(1)=1 as well as a(29)=47 inserted and more terms added by _Michel Marcus_, Oct 26 2013