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A092591
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Exponents n such that 1-A065395(2^n) is a power of 2, where A065395(n) = sigma(phi(n)) - phi(sigma(n)).
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0
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1, 2, 3, 4, 6, 7, 12, 15, 16, 18, 30, 31, 60, 88, 106, 126, 520, 606
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OFFSET
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1,2
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COMMENTS
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LINKS
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EXAMPLE
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At exponents n=1, 3, 7, 15, 31: 1-A065395(2^n)=2.
While at n=2, 4, 6, 12, 16, 18, 30, 60, 88, 106, 126: 1-A065395(2^n)=2^n.
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MATHEMATICA
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f[n_] := DivisorSigma[1, EulerPhi[n]] - EulerPhi[DivisorSigma[1, n]]; pow2Q[n_] := n == 2^IntegerExponent[n, 2]; aQ[n_] := pow2Q[1 - f[2^n]]; Select[Range[130], aQ] (* Amiram Eldar, Aug 22 2019 *)
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PROG
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(PARI) f(n) = sigma(eulerphi(n)) - eulerphi(sigma(n)); \\ A065395
ispp2(k) = isprimepower(k, &p) && (p==2);
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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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