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A230606
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Numbers n such that sigma(n) = k*(n+1) for some integer k.
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3
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2, 3, 5, 7, 11, 13, 17, 19, 20, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 104, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263
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OFFSET
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1,1
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COMMENTS
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Numbers n such that A108775(n) = floor(sigma(n) / n) = sigma(n) mod n = A054024(n).
Union primes (A000040) and composite numbers A045768 (k = 1 for primes p, k = 2 for composite numbers).
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LINKS
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EXAMPLE
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20 is in sequence because sigma(20) = 42 = 2*21.
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MATHEMATICA
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Select[Range[300], Divisible[DivisorSigma[1, #], #+1]&] (* Harvey P. Dale, May 28 2019 *)
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CROSSREFS
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Cf. A045768 (sigma(n) == 2 (mod n)).
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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