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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

Table of n, a(n) for n=1..28.

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

Cf. A000203, A247837, A247820.

Sequence in context: A227172 A180757 A214488 * A159670 A238736 A087511

Adjacent sequences:  A247833 A247834 A247835 * A247837 A247838 A247839

KEYWORD

nonn

AUTHOR

Jaroslav Krizek, Sep 24 2014

STATUS

approved

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Last modified August 8 23:02 EDT 2020. Contains 336300 sequences. (Running on oeis4.)