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 A027761 #18 Jul 08 2025 17:55:18
%S A027761 5,31,41,31,61,3421,5,557,821,371,121,3421,5,929,15745,557,5,2557843,
%T A027761 5,15541,1805,743,241,60887,61,1673,821,929,301,79085411,5,557,66961,
%U A027761 31,4397,188641729,5,31,3281,277727,421,4462547,5,66817,313477,1487,5,5952449
%N A027761 Numerator of sum_{p prime, p-1 divides 2*n} 1/p.
%H A027761 Seiichi Manyama, <a href="/A027761/b027761.txt">Table of n, a(n) for n = 1..10000</a>
%t A027761 a[n_] := Sum[ Boole[ PrimeQ[d+1] ]/(d+1), {d, Divisors[2n]}] // Numerator; Table[a[n], {n, 1, 48}] (* _Jean-François Alcover_, Aug 10 2012 *)
%o A027761 (PARI)
%o A027761 a(n)=
%o A027761 {
%o A027761 my(bd=0);
%o A027761 forprime (p=2, 2*n+1, if( (2*n)%(p-1)==0, bd += 1/p; ) );
%o A027761 bd = numerator(bd);
%o A027761 return(bd);
%o A027761 }
%o A027761 /* _Joerg Arndt_, May 06 2012 */
%Y A027761 Cf. A027762.
%K A027761 nonn,frac
%O A027761 1,1
%A A027761 _N. J. A. Sloane_