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A247820
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Numbers n such that sigma(2n-1) is a prime p.
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11
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5, 13, 145, 365, 841, 1201, 1741, 2521, 3961, 5101, 7813, 8581, 13945, 14281, 14965, 41761, 42925, 73345, 139921, 229165, 245701, 265721, 276025, 289561, 298765, 341965, 351961, 353641, 367225, 414961, 595141, 601705, 676285, 697381, 711625, 740545, 942565
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OFFSET
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1,1
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COMMENTS
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Corresponding values of primes p for a(n) are A008438(a(n)-1)) or A247837.
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LINKS
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EXAMPLE
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Number 13 is in sequence because sigma(2*13-1) = sigma(25) = 31 (prime).
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PROG
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(Magma) [n: n in [1..10000000] | IsPrime(SumOfDivisors(2*n-1))]
(PARI) for(n=1, 10^7, if(isprime(sigma(2*n-1)), print1(n, ", "))) \\ Derek Orr, Sep 25 2014
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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