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A158914
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Primes p such that there is a composite c with sigma_2(p)=sigma_2(c).
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1
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OFFSET
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1,1
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COMMENTS
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No other terms less than 10^8. The corresponding composite numbers are 6, 40, 136, and 3352. Is this sequence finite? See A158913 for the sequence for sigma_1.
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LINKS
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Table of n, a(n) for n=1..4.
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MATHEMATICA
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tp=DivisorSigma[2, Select[Range[4000], PrimeQ]]; tc=DivisorSigma[2, Select[Range[4000], !PrimeQ[ # ]&]]; Sqrt[Intersection[tp, tc]-1]
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CROSSREFS
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Sequence in context: A009219 A158713 A142185 * A046872 A167860 A152988
Adjacent sequences: A158911 A158912 A158913 * A158915 A158916 A158917
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KEYWORD
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more,nonn
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AUTHOR
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T. D. Noe, Mar 30 2009
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STATUS
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approved
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