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A038344
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Numbers k such that phi(k) + sigma(k) is a prime.
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8
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1, 8, 9, 32, 36, 50, 100, 225, 242, 484, 512, 578, 729, 800, 900, 1089, 1156, 1250, 1936, 2025, 2048, 2304, 2312, 2601, 2916, 3025, 3872, 4418, 6400, 7225, 7744, 8192, 8464, 8836, 9216, 10000, 12800, 14400, 20000, 20736, 21609, 26896, 27556, 31684, 32768, 33856, 34322
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OFFSET
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1,2
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COMMENTS
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LINKS
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FORMULA
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EXAMPLE
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a(2) = 8 because phi(8) + sigma(8) = 19.
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MATHEMATICA
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Select[Range[0, 40000], PrimeQ[DivisorSigma[1, #] + EulerPhi[#]] &] (* Vincenzo Librandi, Jul 22 2016 *)
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PROG
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(PARI) isok(n) = isprime(eulerphi(n) + sigma(n)); \\ Michel Marcus, Sep 27 2013
(PARI) v=vector(1000); c=0; for(j=1, 12105, m=j^2; if(isprime(eulerphi(m)+sigma(m)), c++; v[c]=m)); for(j=1, 8559, m=2*j^2; if(isprime(eulerphi(m)+sigma(m)), c++; v[c]=m)); v=vecsort(v); for(n=1, 1000, write("b038344.txt", n " " v[n])) \\ Donovan Johnson, Sep 27 2013
(Magma) [n: n in [1..40000] | IsPrime(EulerPhi(n)+DivisorSigma(1, n))]; // Vincenzo Librandi, Jul 22 2016
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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