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 A066110 #28 Aug 05 2025 06:09:02
%S A066110 13,73,313,601,28393,83233,922561,3416953,13842121,47451433,141146281,
%T A066110 212601841,234750601,294482761,2750006041,3262751521,4362404353,
%U A066110 4784281393,5236041961,9354855121,9597826993,13564461457,16936647121
%N A066110 Primes of the form sigma_4(k)/sigma_2(k), arising in A066109.
%H A066110 Amiram Eldar, <a href="/A066110/b066110.txt">Table of n, a(n) for n = 1..2000</a> (terms 1..250 from Harry J. Smith)
%F A066110 Primes of the form A001159(A066109(k))/A001157(A066109(k)).
%e A066110 For k = 20: divisors(20) = {20,10,5,4,2,1}, sigma_4(20) = 160000 + 10000 + 625 + 256 + 16 + 1 = 170898, sigma_2(20) = 400 + 100 + 25 + 16 + 4 + 1 = 546; p = 170898/546 = 73 is prime, the 2nd term.
%t A066110 Do[s=DivisorSigma[4, n]; z=DivisorSigma[2, n]; If[PrimeQ[s/z], Print[s/z]], {n, 1, 10000000}]
%t A066110 Select[Table[DivisorSigma[4,n]/DivisorSigma[2,n],{n,200000}],PrimeQ] (* _Harvey P. Dale_, Jan 31 2022 *)
%o A066110 (PARI) { n=0; for (m=1, 10^9, if (frac(f=sigma(m, 4)/sigma(m, 2)), next); if (isprime(f), write("b066110.txt", n++, " ", f); if (n==250, return)) ) } \\ _Harry J. Smith_, Feb 01 2010
%Y A066110 Cf. A000040, A001157, A001159, A066109, A066111, A066112.
%K A066110 nonn
%O A066110 1,1
%A A066110 _Labos Elemer_, Dec 05 2001