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

3, 7, 13, 31, 127

Offset: 1

Author

Jaroslav Krizek, Jan 16 2015

Keywords

• nonn
• more

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 greater than A000043(48) = 57885161, and also not equal to any of the Mersenne prime exponents 74207281, 77232917, 82589933, 136279841. - Gord Palameta, Oct 22 2024

Examples

			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.
		

Crossrefs

Cf. A000043, A000203, A000668, A023195, A253849, A253851.

Programs

Magma

Set(Sort([SumOfDivisors(n): n in[1..10000] | IsPrime((2^SumOfDivisors(n))- 1)]));