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A065875 Usigma(Phi(n)) is a prime. 1
3, 4, 5, 6, 8, 10, 12, 17, 32, 34, 40, 48, 60, 257, 512, 514, 544, 640, 680, 768, 816, 960, 1020, 65537, 131072, 131074, 131584, 139264, 139808, 163840, 164480, 174080, 174760, 196608, 197376, 208896, 209712, 245760, 246720, 261120, 262140 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

n is odd for only 3, 5, 17, 257 & 65537 for n < 10^7; they being the Fermat primes.

LINKS

Table of n, a(n) for n=1..41.

MATHEMATICA

f[n_] := Block[ {a = FactorInteger[n], k = l = s = 1}, l = Length[a]; While[k <= l, s = s * (a[[k, 1]]^a[[k, 2]] + 1); k++ ]; Return[s]]; Select[ Range[10^7], PrimeQ[ f[ EulerPhi[ # ]]] & ]

CROSSREFS

Cf. A062514.

Sequence in context: A180646 A300217 A062514 * A197639 A319314 A167057

Adjacent sequences:  A065872 A065873 A065874 * A065876 A065877 A065878

KEYWORD

nonn

AUTHOR

Robert G. Wilson v, Dec 07 2001

STATUS

approved

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Last modified January 25 01:49 EST 2020. Contains 331229 sequences. (Running on oeis4.)