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A247836 Primes p of the form sigma(2q-1) where q is a prime. 2
13, 31, 2801, 3541, 5113, 10303, 17293, 30941, 88741, 292561, 732541, 1191373, 1395943, 2922391, 3281533, 7450171, 7781311, 12190573, 15916111, 22292563, 28792661, 67757593, 93886411, 103052953, 112137511, 124802413, 135059263, 181427431 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Subsequence of A247837.
LINKS
EXAMPLE
Prime 13 is in sequence because there is prime 5 such that sigma(2*5-1) = sigma(9) = 13.
PROG
(Magma) Sort([a: p in PrimesUpTo(5000000) | IsPrime(a) where a is SumOfDivisors(2*p-1)]) # corrected by Jaroslav Krizek, Nov 16 2014
(PARI) forprime(p=1, 10^9, if(isprime(sigma(2*p-1)), print1(sigma(2*p-1), ", "))) \\ Derek Orr, Sep 25 2014
CROSSREFS
Sequence in context: A227172 A180757 A214488 * A159670 A238736 A087511
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Sep 24 2014
STATUS
approved

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Last modified May 21 22:16 EDT 2024. Contains 372741 sequences. (Running on oeis4.)