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Numerator of sum_{p prime, p-1 divides 2*n} 1/p.
3

%I #16 Sep 26 2016 06:15:06

%S 5,31,41,31,61,3421,5,557,821,371,121,3421,5,929,15745,557,5,2557843,

%T 5,15541,1805,743,241,60887,61,1673,821,929,301,79085411,5,557,66961,

%U 31,4397,188641729,5,31,3281,277727,421,4462547,5,66817,313477,1487,5,5952449

%N Numerator of sum_{p prime, p-1 divides 2*n} 1/p.

%H Seiichi Manyama, <a href="/A027761/b027761.txt">Table of n, a(n) for n = 1..10000</a>

%t 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 (PARI)

%o a(n)=

%o {

%o my(bd=0);

%o forprime (p=2, 2*n+1, if( (2*n)%(p-1)==0, bd += 1/p; ) );

%o bd = numerator(bd);

%o return(bd);

%o }

%o /* _Joerg Arndt_, May 06 2012 */

%Y Cf. A027762.

%K nonn,frac

%O 1,1

%A _N. J. A. Sloane_.