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 A247789 Primes p such that sigma(2p-1) is a prime q. 2
 5, 13, 1201, 1741, 2521, 5101, 8581, 14281, 41761, 139921, 353641, 595141, 697381, 1460341, 1639861, 3723721, 3889261, 6093541, 7956061, 11143921, 14199121, 33874681, 46938361, 51521401, 56063461, 62395621, 67523821, 90706981 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Subsequence of A247820. Corresponding values of primes q for a(n) are in A247836. LINKS EXAMPLE Prime 13 is in sequence because sigma(2*13-1) = sigma(25) = 31 (prime). PROG (MAGMA) [p: p in PrimesUpTo(50000000) | IsPrime(SumOfDivisors(2*p-1))] (PARI) forprime(p=1, 10^9, if(isprime(sigma(2*p-1)), print1(p, ", "))) \\ Derek Orr, Sep 25 2014 CROSSREFS Cf. A000203, A008438, A000203, A247820. Sequence in context: A155185 A009157 A153374 * A012032 A121228 A201260 Adjacent sequences:  A247786 A247787 A247788 * A247790 A247791 A247792 KEYWORD nonn AUTHOR Jaroslav Krizek, Sep 24 2014 STATUS approved

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