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A063830
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a(n+1) is the smallest odd m whose cototient equals a(n).
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0
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1, 3, 9, 21, 45, 117, 297, 585, 1521, 3105, 6993, 14553, 43653, 90885, 185925, 397125, 847125, 1813125, 3238725, 7556829, 17253789, 36910365, 94571997, 220301277, 475043037, 47979336637, 183450404605, 525019294077
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OFFSET
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1,2
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LINKS
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FORMULA
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a(n) = Min{x, odd : A051953[ a(n-1) ]=a(n)}; a(1)=1; a(2)=3, least odd prime; a(n) = Min[ Select[ Range[ a, b ], Equal[ #-EulerPhi[ # ], a(n-1) ]& ] ].
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EXAMPLE
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a(5)=45, cototient(45) = 45 - Phi(45) = 45 - 24 = 21 = a(4). This iteration with even numbers might stop, like {1,2,4,6,10} does if the last computed number has no inverse cototient, like 10 which is a non-cototient number.
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CROSSREFS
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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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