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Search: id:A065872
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| A065872 |
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Numbers n such that usigma(n) - 1 is a prime (cf. A034448). |
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+0
1
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| 2, 3, 5, 6, 7, 10, 11, 12, 13, 14, 15, 17, 18, 19, 20, 21, 23, 26, 29, 30, 31, 33, 34, 35, 37, 38, 40, 41, 43, 44, 45, 46, 47, 48, 51, 53, 54, 55, 56, 57, 58, 59, 61, 63, 65, 67, 68, 71, 72, 73, 74, 75, 78, 79, 80, 83, 85, 86, 88, 89, 90, 93, 96, 97, 98, 101, 103, 105, 107
(list; graph; listen)
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OFFSET
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1,1
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LINKS
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Harry J. Smith, Table of n, a(n) for n=1,...,1000
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MATHEMATICA
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f[n_] := Block[ {a = FactorInteger[n], k = l = s = 1}, l = Length[a]; While[k <= l, s = s * (a[[k, 1]]^a[[k, 2]] + 1); k++ ]; Return[s]]; Select[ Range[200], PrimeQ[ f[ # ] - 1] & ]
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PROGRAM
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(PARI) usigma(n)= { local(f, s=1); f=factor(n); for(i=1, matsize(f)[1], s*=1 + f[i, 1]^f[i, 2]); return(s) } { n=0; for (m=1, 10^9, if (isprime(usigma(m) - 1), write("b065872.txt", n++, " ", m); if (n==1000, return)) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Nov 02 2009]
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CROSSREFS
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Cf. A034448.
Sequence in context: A007916 A052485 A109421 this_sequence A028741 A119316 A102750
Adjacent sequences: A065869 A065870 A065871 this_sequence A065873 A065874 A065875
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KEYWORD
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nonn
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AUTHOR
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Robert G. Wilson v (rgwv(AT)rgwv.com), Dec 07 2001
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