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Search: id:A066814
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| A066814 |
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Smallest prime p so that (p-1) has n divisors, or 0 if no such prime exists. |
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+0
2
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| 2, 3, 5, 7, 17, 13, 0, 31, 37, 113, 0, 61, 0, 193, 401, 211, 65537, 181, 0, 241, 577, 13313, 0, 421, 1297, 12289, 4357, 2113, 0, 1009, 0, 1321, 25601, 2424833, 752734097, 1801, 0, 786433, 495617, 2161, 0, 4801, 0, 15361, 7057, 155189249, 0
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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The only primes p < 7.10^8 for which p-1 has a prime number of divisors are 2,3,5,17
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EXAMPLE
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a(17)=65537 because DivisorSigma[0,65536]=17.
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MATHEMATICA
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it=Table[ p=Prime[ n ]; DivisorSigma[ 0, p-1 ], {n, 400000} ]; Flatten[ Position[ it, #, 1, 1 ]&/@Range[ 100 ]/.{}- > 0 ]
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CROSSREFS
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Cf. A004249, A007516, A066529.
Sequence in context: A145968 A059471 A059496 this_sequence A072885 A042994 A129692
Adjacent sequences: A066811 A066812 A066813 this_sequence A066815 A066816 A066817
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KEYWORD
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hard,nonn
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AUTHOR
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Wouter Meeussen (wouter.meeussen(AT)pandora.be), Jan 20 2002
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