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A072868
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Numbers k such that sigma(sigma(k) - k) = k.
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10
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OFFSET
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1,1
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COMMENTS
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Because numbers of the form 1+A000668(.) are a subsequence, 162259276829213363391578010288128 and 170141183460469231731687303715884105728 are also in the sequence (not necessarily the next ones). - Joerg Arndt, Jul 01 2012
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LINKS
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FORMULA
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a(n) = 1 + A000668(n) (conjecture), which implies equivalent conjectures stated in A000668.
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MATHEMATICA
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Select[Range[550000], DivisorSigma[1, DivisorSigma[1, #]-#]==#&] (* The program generates the first 7 terms of the sequence. Increasing the Range constant will generate more but it will run a long time. *) (* Harvey P. Dale, May 08 2018 *)
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PROG
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(PARI) isok(n) = sigma(sigma(n)-n) == n; \\ Michel Marcus, May 06 2016
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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