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A004169
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Values of m for which a regular polygon with m sides cannot be constructed with ruler and compass.
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14
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7, 9, 11, 13, 14, 18, 19, 21, 22, 23, 25, 26, 27, 28, 29, 31, 33, 35, 36, 37, 38, 39, 41, 42, 43, 44, 45, 46, 47, 49, 50, 52, 53, 54, 55, 56, 57, 58, 59, 61, 62, 63, 65, 66, 67, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 81, 82, 83, 84, 86, 87, 88, 89, 90, 91
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OFFSET
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1,1
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COMMENTS
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Numbers m for which phi(a(m)) is not a power of 2, phi = A000010, Euler's totient function. - Reinhard Zumkeller, Jul 31 2012
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REFERENCES
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A. H. Beiler, Recreations in the Theory of Numbers, Dover, NY, 1964, p. 183.
B. L. van der Waerden, Modern Algebra. Unger, NY, 2nd ed., Vols. 1-2, 1953, Vol. 1, p. 187.
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LINKS
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Claudi Alsina and Roger B. Nelson, A Panoply of Polygons, Dolciani Math. Expeditions Vol. 58, AMS/MAA (2023), see page 16.
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FORMULA
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MATHEMATICA
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PROG
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(Haskell)
a004169 n = a004169_list !! (n-1)
a004169_list = map (+ 1) $ elemIndices 0 $ map a209229 a000010_list
(PARI) is(n)=my(t=4294967295); n>>=valuation(n, 2); n/=gcd(n, t); if(gcd(n, t)>1, return(1)); if(n==1, return(0)); if(n<9e2585827972, return(1)); forprime(p=7, 1e5, if(n%p==0, return(1))); warning("Result is conjectural on the nonexistence of Fermat primes >= F(33)."); 1 \\ Charles R Greathouse IV, Oct 23 2015
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CROSSREFS
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KEYWORD
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nonn,nice
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AUTHOR
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STATUS
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approved
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