A253850 Mersenne exponents (A000043) that are the sum of the divisors (A000203) of some n.

3, 7, 13, 31, 127

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