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A268130
Primes p of the form sigma(2^k + 1) - 1 for some k >= 0.
1
2, 3, 5, 17, 47, 83, 257, 1301, 65537, 174767, 5048231, 51322664447, 188313058624991, 4768522825659911, 3148244377723715041631, 211635519858089932125000235391, 906780938207203620571208267879698943, 6392739029893008727817055462596999999
OFFSET
1,1
COMMENTS
Corresponding values of k: 0, 1, 2, 4, 5, 6, 8, 10, 16, 17, 22, 35, 47, 52, 71, 97, 119, 122, 124, 190, 300, ...
Fermat primes from A019434 are in the sequence.
LINKS
EXAMPLE
Prime 47 is a term because for k = 5, sigma(2^5+1) - 1 = sigma(33) - 1 = 47.
PROG
(Magma) Set(Sort([SumOfDivisors(2^n+1)-1: n in [0..300] | IsPrime(SumOfDivisors(2^n+1)-1)]));
(PARI) lista(nn) = for (n=0, nn, if (isprime(p=sigma(2^n + 1) - 1), print1(p, ", "))); \\ Michel Marcus, Jan 27 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Jan 26 2016
STATUS
approved