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 A253850 Mersenne exponents (A000043) that are the sum of the divisors (A000203) of some n. 4
 3, 7, 13, 31, 127 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Also primes p that are the sum of the divisors of some n where 2^sigma(n) - 1 is a Mersenne prime (A000668). Intersection of A023195 and A000043. If a(6) exists, it must be bigger than A000043(43) = 30402457. LINKS Table of n, a(n) for n=1..5. EXAMPLE Mersenne exponent 7 is in the sequence because sigma(4) = 7. Mersenne exponent 31 is in the sequence because there are two numbers n (16 and 25) with sigma(n) = 31. PROG (Magma) Set(Sort([SumOfDivisors(n): n in[1..10000] | IsPrime((2^SumOfDivisors(n))- 1)])) CROSSREFS Cf. A000043, A000203, A000668, A023195, A253849, A253851. Sequence in context: A077314 A069246 A340870 * A087578 A023195 A100382 Adjacent sequences: A253847 A253848 A253849 * A253851 A253852 A253853 KEYWORD nonn,more AUTHOR Jaroslav Krizek, Jan 16 2015 STATUS approved

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Last modified August 9 04:25 EDT 2024. Contains 375027 sequences. (Running on oeis4.)