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A058321
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Number of x such that phi(x) = 2^n.
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2
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2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32
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OFFSET
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0,1
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COMMENTS
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The first unknown term is a(8589934592) which depends on whether A000215(33) is composite or prime. - Jeppe Stig Nielsen, Oct 02 2021
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LINKS
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FORMULA
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EXAMPLE
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For n = 0, a(0) = 2 because phi(1) = phi(2) = 1.
For n = 5, invphi(32) gives 7 values as follows: Phi[{51,64,68,80,96,102,120}] = {32,32,32,32,32,32,32}.
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MAPLE
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with(numtheory):[seq(nops(invphi(2^i)), i=1..100)];
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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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Added a(0) and corrected a(31) - T. D. Noe, Jun 21 2012
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STATUS
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approved
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