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A292369
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Numbers n such that f(f(f(n))) = f(f(n)) + f(n) where f = A000203.
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0
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OFFSET
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1,1
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COMMENTS
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Are there any odd terms other than 25?
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LINKS
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EXAMPLE
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25 = 5^2 is a term because sigma(sigma(sigma(5^2))) = sigma(2^5) = sigma(sigma(5^2)) + sigma(5^2).
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MATHEMATICA
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f[n_] := DivisorSigma[1, n]; fQ[n_] := f[f[f[n]]] == f[f[n]] + f[n]; Select[ Range@1000000, fQ] (* Robert G. Wilson v, Sep 23 2017 *)
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PROG
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(PARI) s(n) = sigma(n);
isok(n) = s(s(s(n)))==s(s(n))+s(n);
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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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