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 A348659 #11 Oct 28 2021 10:01:24
%S A348659 3,5,13,14,15,37,42,61,66,73,92,114,157,182,193,258,277,308,313,397,
%T A348659 402,421,457,476,477,541,546,570,613,661,673,733,744,757,812,877,978,
%U A348659 997,1093,1148,1153,1201,1213,1237,1266,1278,1321,1381,1428,1453,1621,1657
%N A348659 Numbers whose numerator and denominator of the harmonic mean of their divisors are both prime numbers.
%C A348659 The prime terms of this sequence are the primes p such that (p+1)/2 is also a prime (A005383).
%C A348659 If p is in A109835, then p*(2*p-1) is a semiprime term.
%H A348659 Amiram Eldar, <a href="/A348659/b348659.txt">Table of n, a(n) for n = 1..10000</a>
%e A348659 3 is a term since the harmonic mean of its divisors is 3/2 and both 2 and 3 are primes.
%t A348659 q[n_] := Module[{h = DivisorSigma[0, n]/DivisorSigma[-1, n]}, And @@ PrimeQ[{Numerator[h], Denominator[h]}]]; Select[Range[2000], q]
%Y A348659 Cf. A005383, A099377, A099378, A109835.
%Y A348659 Similar sequences: A023194, A048968, A074266, A348659.
%K A348659 nonn
%O A348659 1,1
%A A348659 _Amiram Eldar_, Oct 28 2021