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A079446
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Integers k such that phi(k)*(k-phi(k))+1 is prime.
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3
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2, 3, 4, 5, 7, 8, 9, 11, 13, 17, 18, 19, 20, 21, 23, 25, 27, 28, 29, 31, 32, 37, 41, 43, 47, 50, 52, 53, 55, 56, 57, 59, 61, 67, 68, 71, 72, 73, 77, 78, 79, 81, 83, 89, 92, 95, 97, 99, 101, 103, 104, 107, 108, 109, 110, 113, 115, 116, 127, 131, 137, 139, 145
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OFFSET
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1,1
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COMMENTS
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Includes all primes. - Robert Israel, Oct 25 2017
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LINKS
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Robert Israel, Table of n, a(n) for n = 1..10000
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EXAMPLE
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phi(8)=4, so 4*(8-4)+1=17.
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MAPLE
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filter:= proc(n) local p;
p:= numtheory:-phi(n);
isprime(p*(n-p)+1)
end proc:
select(filter, [$1..1000]); # Robert Israel, Oct 25 2017
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MATHEMATICA
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Select[Range[150], PrimeQ[EulerPhi[#]*(# - EulerPhi[#]) + 1] &] (* G. C. Greubel, Jan 18 2019 *)
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PROG
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(PARI) for (n=2, 100, if (isprime(eulerphi(n)*(n-eulerphi(n))+1), print1(n", ")))
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CROSSREFS
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Cf. A079445.
Sequence in context: A038701 A127072 A056781 * A322546 A283262 A115975
Adjacent sequences: A079443 A079444 A079445 * A079447 A079448 A079449
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KEYWORD
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nonn
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AUTHOR
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Jon Perry, Jan 09 2003
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EXTENSIONS
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More terms from Michel Marcus, Mar 17 2014
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STATUS
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approved
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