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A268130 Primes p of the form sigma(2^n + 1) - 1 for some n >= 0. 1
2, 3, 5, 17, 47, 83, 257, 1301, 65537, 174767, 5048231, 51322664447, 188313058624991, 4768522825659911, 3148244377723715041631, 211635519858089932125000235391, 906780938207203620571208267879698943, 6392739029893008727817055462596999999 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Corresponding values of n: 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

Jaroslav Krizek, Table of n, a(n) for n = 1..21

EXAMPLE

Prime 47 is term because there is number n = 5 such that 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

Cf. A000051, A000203, A069061, A019434.

Sequence in context: A019350 A235630 A235636 * A103074 A173236 A268209

Adjacent sequences:  A268127 A268128 A268129 * A268131 A268132 A268133

KEYWORD

nonn

AUTHOR

Jaroslav Krizek, Jan 26 2016

STATUS

approved

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Last modified October 20 04:37 EDT 2019. Contains 328247 sequences. (Running on oeis4.)