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A066071
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Nonprime numbers n such that Phi[n] + 1 is prime.
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13
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1, 4, 6, 8, 9, 10, 12, 14, 18, 21, 22, 26, 27, 28, 32, 34, 36, 38, 40, 42, 46, 48, 49, 54, 55, 57, 58, 60, 62, 63, 74, 75, 76, 77, 82, 86, 88, 91, 93, 94, 95, 98, 99, 100, 106, 108, 110, 111, 114, 115, 117, 118, 119, 122, 124, 125, 126, 132, 133, 134, 135, 142, 145, 146
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| A039698 with the primes removed. For every prime p, 2p is in the sequence. - Ray Chandler (rayjchandler(AT)sbcglobal.net), May 26 2008
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LINKS
| Harry J. Smith, Table of n, a(n) for n=1,...,1000
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EXAMPLE
| Solutions to 1+Phi[x]=13 are {13, 21, 26, 28, 36, 42} of which the 5 composites are in the sequence.
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PROG
| (PARI) { n=0; for (m=1, 10^9, if (!isprime(m) && isprime(eulerphi(m) + 1), write("b066071.txt", n++, " ", m); if (n==1000, return)) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Nov 10 2009]
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CROSSREFS
| Cf. A000010, A000040, A006093, A039649, A039698, A066071-A066080.
Sequence in context: A129930 A128510 A109289 * A067013 A141607 A071070
Adjacent sequences: A066068 A066069 A066070 * A066072 A066073 A066074
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KEYWORD
| nonn
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AUTHOR
| Labos E. (labos(AT)ana.sote.hu), Dec 03 2001
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