This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A253850 #22 Nov 06 2024 05:00:02 %S A253850 3,7,13,31,127 %N A253850 Mersenne exponents (A000043) that are the sum of the divisors (A000203) of some n. %C A253850 Also primes p that are the sum of the divisors of some n where 2^sigma(n) - 1 is a Mersenne prime (A000668). %C A253850 Intersection of A023195 and A000043. %C A253850 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 %e A253850 Mersenne exponent 7 is in the sequence because sigma(4) = 7. %e A253850 Mersenne exponent 31 is in the sequence because there are two numbers n (16 and 25) with sigma(n) = 31. %o A253850 (Magma) Set(Sort([SumOfDivisors(n): n in[1..10000] | IsPrime((2^SumOfDivisors(n))- 1)])); %Y A253850 Cf. A000043, A000203, A000668, A023195, A253849, A253851. %K A253850 nonn,more %O A253850 1,1 %A A253850 _Jaroslav Krizek_, Jan 16 2015