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A158913
Primes p such that there is a composite c with sigma(p) = sigma(c).
8
11, 17, 23, 31, 41, 47, 53, 59, 71, 79, 83, 89, 97, 103, 107, 113, 127, 131, 139, 151, 167, 179, 181, 191, 223, 227, 233, 239, 251, 263, 269, 271, 293, 307, 311, 359, 383, 389, 419, 431, 433, 439, 443, 449, 467, 479, 491, 503, 521, 557, 569, 571, 587, 593, 599
OFFSET
1,1
COMMENTS
See A158914 for the sequence for sigma_2.
LINKS
MATHEMATICA
tp=DivisorSigma[1, Select[Range[1000], PrimeQ]]; tc=DivisorSigma[1, Select[Range[1000], !PrimeQ[ # ]&]]; Intersection[tp, tc]-1
PROG
(Sage) [sigma(n)-1 for n in (2..600) if is_prime(sigma(n)-1) and n<sigma(n)-1<600] # Giuseppe Coppoletta, Dec 22 2014
CROSSREFS
Sequence in context: A006621 A337359 A275596 * A363638 A066938 A219602
KEYWORD
nonn
AUTHOR
T. D. Noe, Mar 30 2009
STATUS
approved