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 A027761 Numerator of sum_{p prime, p-1 divides 2*n} 1/p. 3
 5, 31, 41, 31, 61, 3421, 5, 557, 821, 371, 121, 3421, 5, 929, 15745, 557, 5, 2557843, 5, 15541, 1805, 743, 241, 60887, 61, 1673, 821, 929, 301, 79085411, 5, 557, 66961, 31, 4397, 188641729, 5, 31, 3281, 277727, 421, 4462547, 5, 66817, 313477, 1487, 5, 5952449 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Seiichi Manyama, Table of n, a(n) for n = 1..10000 MATHEMATICA 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 *) PROG (PARI) a(n)= { my(bd=0); forprime (p=2, 2*n+1, if( (2*n)%(p-1)==0, bd += 1/p; ) ); bd = numerator(bd); return(bd); } /* Joerg Arndt, May 06 2012 */ CROSSREFS Cf. A027762. Sequence in context: A042837 A354881 A162173 * A166306 A341632 A287300 Adjacent sequences: A027758 A027759 A027760 * A027762 A027763 A027764 KEYWORD nonn,frac AUTHOR STATUS approved

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Last modified January 29 11:47 EST 2023. Contains 359922 sequences. (Running on oeis4.)