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A027761
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Numerator of sum_{p prime, p-1 divides 2*n} 1/p.
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3
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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
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OFFSET
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1,1
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LINKS
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MATHEMATICA
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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 *)
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PROG
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(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);
}
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CROSSREFS
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KEYWORD
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nonn,frac
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AUTHOR
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STATUS
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approved
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