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A055744
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Numbers n such that n and phi(n) have same prime factors.
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5
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1, 4, 8, 16, 18, 32, 36, 50, 54, 64, 72, 100, 108, 128, 144, 162, 200, 216, 250, 256, 288, 294, 324, 400, 432, 450, 486, 500, 512, 576, 578, 588, 648, 800, 864, 882, 900, 972, 1000, 1014, 1024, 1152, 1156, 1176, 1210, 1250, 1296, 1350, 1458, 1600, 1728, 1764
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Contains products of suitable powers of 2 and Fermat primes. For x=2^u.3^w, Phi(x)=2^u.3^(w-1) with suitable exponents. Analogous constructions are possible with {2,3,7} prime divisors, etc.
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LINKS
| T. D. Noe, Table of n, a(n) for n = 1..1000
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EXAMPLE
| n=578=2.17.17, phi(578)=272=2.2.2.2.17 with 2 and 17 prime-factors n=588=2.2.3.7.7, phi(588)=168=2.2.2.3.7 n=264196=2.2.257.257, phi(264196)=512.257=131584
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PROG
| (PARI) is(n)=vecsort(factor(n)[, 1])==vecsort(factor(eulerphi(n))[, 1]) \\ Charles R Greathouse IV, Oct 31 2011
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CROSSREFS
| Cf. A001221, A000010.
Cf. A110751, A110819, A027598, A081377.
Sequence in context: A195065 A070738 * A141718 A195382 A181310 A033310
Adjacent sequences: A055741 A055742 A055743 * A055745 A055746 A055747
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KEYWORD
| nonn
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AUTHOR
| Labos E. (labos(AT)ana.sote.hu), Jul 11 2000
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EXTENSIONS
| Corrected and extended by James A. Sellers (sellersj(AT)math.psu.edu), Jul 11 2000
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