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A141056
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1 followed by A027760, a variant of Bernoulli number denominators.
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25
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1, 2, 6, 2, 30, 2, 42, 2, 30, 2, 66, 2, 2730, 2, 6, 2, 510, 2, 798, 2, 330, 2, 138, 2, 2730, 2, 6, 2, 870, 2, 14322, 2, 510, 2, 6, 2, 1919190, 2, 6, 2, 13530, 2, 1806, 2, 690, 2, 282, 2, 46410, 2, 66, 2, 1590, 2, 798, 2, 870, 2, 354, 2, 56786730, 2, 6, 2, 510, 2, 64722, 2, 30, 2, 4686
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OFFSET
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0,2
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COMMENTS
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The denominators of the Bernoulli numbers for n>0. B_n sequence begins 1, -1/2, 1/6, 0/2, -1/30, 0/2, 1/42, 0/2, ... This is an alternative version of A027642 suggested by the theorem of Clausen. [From Peter Luschny, Apr 29 2009]
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LINKS
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Table of n, a(n) for n=0..70.
Thomas Clausen, Lehrsatz aus einer Abhandlung Ueber die Bernoullischen Zahlen, Astr. Nachr. 17 (22) (1840), 351-352.
Wikipedia, Bernoulli number
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MAPLE
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Clausen := proc(n) local S, i;
S := numtheory[divisors](n); S := map(i->i+1, S);
S := select(isprime, S); mul(i, i=S) end proc:
seq(Clausen(i), i=0..24);
# Peter Luschny, Apr 29 2009
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MATHEMATICA
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a[n_] := Sum[ Boole[ PrimeQ[d+1]] / (d+1), {d, Divisors[n]}] // Denominator; Table[a[n], {n, 0, 70}] (* Jean-François Alcover, Aug 09 2012 *)
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PROG
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(Pari)
A141056(n) =
{
p = 1;
if (n > 0,
fordiv(n, d,
r = d + 1;
if (isprime(r), p = p*r)
)
);
return(p)
}
for(n=0, 70, print1(A141056(n), ", ")); /* Peter Luschny, May 07 2012 */
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CROSSREFS
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Cf. A027760, A027642.
Sequence in context: A076743 A217448 A027760 * A141498 A225481 A144845
Adjacent sequences: A141053 A141054 A141055 * A141057 A141058 A141059
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KEYWORD
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nonn
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AUTHOR
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Paul Curtz, Aug 01 2008
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EXTENSIONS
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Extended by R. J. Mathar, Nov 22 2009
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STATUS
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approved
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