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 A253851 Mersenne primes (A000668) of the form 2^sigma(n) - 1 for some n. 2
 7, 127, 8191, 2147483647, 170141183460469231731687303715884105727 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers n such that 2^sigma(n) - 1 is a Mersenne primes are given in A253849. Sequence of corresponding values of sigma(n) are given in A253850 and each term of this sequence must be a prime from the sequence of Mersenne exponents (A000043). If a(6) exists, it must be bigger than A000668(43) = 2^30402457-1. LINKS EXAMPLE Mersenne prime 2147483647 is in the sequence because there are two numbers n (16 and 25) with 2^sigma(n) - 1 = 2^31 - 1 = 2147483647. PROG (MAGMA) Set(Sort([(2^SumOfDivisors(n))-1: n in[1..10000] | IsPrime((2^SumOfDivisors(n))-1)])) CROSSREFS Cf. A000043, A000203, A000668, A023195, A253849, A253850. Sequence in context: A138523 A034670 A020516 * A077585 A261487 A134722 Adjacent sequences:  A253848 A253849 A253850 * A253852 A253853 A253854 KEYWORD nonn AUTHOR Jaroslav Krizek, Jan 16 2015 STATUS approved

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Last modified October 26 08:06 EDT 2020. Contains 338027 sequences. (Running on oeis4.)