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 A027759 #25 Jul 08 2025 17:55:11
%S A027759 1,5,1,31,1,41,1,31,1,61,1,3421,1,5,1,557,1,821,1,371,1,121,1,3421,1,
%T A027759 5,1,929,1,15745,1,557,1,5,1,2557843,1,5,1,15541,1,1805,1,743,1,241,1,
%U A027759 60887,1,61,1,1673,1,821,1,929,1,301,1,79085411,1,5,1,557
%N A027759 Numerator of Sum_{p prime, p-1|n} 1/p.
%H A027759 John Cerkan, <a href="/A027759/b027759.txt">Table of n, a(n) for n = 1..10000</a>
%F A027759 a(2n-1) = 1 and a(2n) = A000146(n)* A002445(n) - A000367(n) for n > 0. - _Thomas Ordowski_, May 06 2021
%e A027759 1/2, 5/6, 1/2, 31/30, 1/2, 41/42, 1/2, 31/30, 1/2, 61/66, 1/2, 3421/2730, 1/2, 5/6, 1/2, 557/510, ...
%t A027759 a[n_] := 1/(Select[Divisors[n], PrimeQ[# + 1]&] + 1) // Total // Numerator;
%t A027759 Array[a, 100] (* _Jean-François Alcover_, Sep 20 2020 *)
%o A027759 (PARI) a(n) = numerator(sumdiv(n, d, if (isprime(d+1), 1/(d+1)))); \\ _Michel Marcus_, May 06 2021
%Y A027759 Cf. A027760 (denominator).
%K A027759 nonn,frac
%O A027759 1,2
%A A027759 _N. J. A. Sloane_
%E A027759 a(57)-a(64) from _John Cerkan_, Mar 21 2018