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A246858
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Composite numbers k such that sigma(k + sigma(k)) = 2*sigma(k).
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2
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329, 413, 623, 869, 979, 1819, 2585, 3107, 3173, 3197, 3887, 4235, 4997, 5771, 6149, 6187, 6443, 7409, 8399, 8759, 14429, 15323, 18515, 19019, 21181, 21413, 23989, 26491, 29749, 30355, 31043, 32623, 34009, 34177, 39737, 47321, 47845, 51389, 53311, 56419
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OFFSET
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1,1
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COMMENTS
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Complement of A005384 (Sophie Germain primes) with respect to A246857.
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LINKS
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EXAMPLE
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Number 329 (with sigma(329) = 384) is in sequence because sigma(329 + sigma(329)) = sigma(713) = 768 = 2*384.
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MATHEMATICA
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Select[Range[57000], And[CompositeQ[#], DivisorSigma[1, # + DivisorSigma[1, #]] == 2 DivisorSigma[1, #]] &] (* Michael De Vlieger, Aug 05 2021 *)
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PROG
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(Magma) [n:n in[1..1000] | SumOfDivisors(n+SumOfDivisors(n)) eq 2*SumOfDivisors(n) and not IsPrime(n)]
(PARI) lista(nn) = {forcomposite(n=2, nn, if (sigma(n+sigma(n)) == 2*sigma(n), print1(n, ", ")); ); } \\ Michel Marcus, Sep 05 2014
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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