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A246914
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Primes p such that sigma(2p+1) = 3*(p+1).
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6
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OFFSET
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1,1
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COMMENTS
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Primes p such that sigma(p+sigma(p)) = 3*sigma(p). Subsequence of A246910.
The next term, if it exists, must be greater than 10^9.
Conjecture: Also primes p such that sigma(2p+1) mod p = 3. - Jaroslav Krizek, Sep 28 2014
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LINKS
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EXAMPLE
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Prime 7 is in sequence because sigma(2*7 + 1) = sigma(15) = 24 = 3*(7+1).
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MAPLE
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MATHEMATICA
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Select[Prime[Range[1500]], DivisorSigma[1, 2# + 1] == 3# + 3 &] (* Alonso del Arte, Sep 07 2014 *)
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PROG
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(Magma) [n:n in[1..10^7] | SumOfDivisors(n+SumOfDivisors(n))eq 3*SumOfDivisors(n) and IsPrime(n)]
(PARI)
for(n=1, 10^6, p=prime(n); if(sigma(p+sigma(p))==3*sigma(p), print1(p, ", "))) \\ Derek Orr, Sep 07 2014
(PARI) forprime(p=2, 10^7, if(sigma(2*p+1)==3*(p+1), print1(p, ", "))) \\ Edward Jiang, Sep 07 2014
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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STATUS
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approved
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