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A075863
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Numbers k such that phi(phi(k)) = sum of prime factors of k.
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0
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8, 45, 55, 95, 126, 132, 198, 215, 228, 516, 2855, 6852, 7655, 18372, 276455, 663492
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OFFSET
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1,1
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COMMENTS
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LINKS
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EXAMPLE
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phi(phi(126)) = phi(36) = 12 and the sum of the prime factors of 126 = 2 * 3^2 * 7 is 2 + 3 + 7 = 12. Hence 126 belongs to the sequence.
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MATHEMATICA
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Select[Range[2, 10^5], EulerPhi[EulerPhi[ # ]] == Apply[Plus, Transpose[FactorInteger[ # ]][[1]]] &]
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PROG
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(Python)
from sympy import primefactors, totient as phi
def ok(n): return n and phi(phi(n)) == sum(primefactors(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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