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Search: id:A075227
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| A075227 |
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Smallest odd prime not occurring in the numerator of the 2^n sums generated from the set 1, 1/2, 1/3,..., 1/n. |
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+0
4
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| 3, 5, 7, 17, 37, 43, 43, 151, 151, 409, 491, 491, 491, 1087, 2011, 3709, 3709, 7417, 7417, 7417
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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The largest prime generated is given in A075226. For information about how often the numerator of these sums is prime, see A075188 and A075189.
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EXAMPLE
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a(3) = 7 because 7 is the smallest prime not occurring in the numerator of the sums 1+1/2 = 3/2, 1/2+1/3 = 5/6 and 1+1/2+1/3 = 11/6.
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MATHEMATICA
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Needs["DiscreteMath`Combinatorica`"]; maxN=20; For[lst={}; prms={}; i=0; n=1, n<=maxN, n++, While[i<2^n-1, i++; s=NthSubset[i, Range[n]]; k=Numerator[Plus@@(1/s)]; If[PrimeQ[k], AppendTo[prms, k]]]; prms=Union[prms]; j=2; While[MemberQ[prms, Prime[j]], j++ ]; AppendTo[lst, Prime[j]]]; lst
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CROSSREFS
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Cf. A001008, A075135, A075188, A075189, A075226.
Adjacent sequences: A075224 A075225 A075226 this_sequence A075228 A075229 A075230
Sequence in context: A016041 A140797 A038893 this_sequence A064080 A112986 A088732
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KEYWORD
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nice,nonn
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AUTHOR
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T. D. Noe (noe(AT)sspectra.com), Sep 08 2002
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