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A158913 Primes p such that there is a composite c with sigma(p)=sigma(c). 4
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

See A158914 for the sequence for sigma_2.

LINKS

Table of n, a(n) for n=1..55.

MATHEMATICA

tp=DivisorSigma[1, Select[Range[1000], PrimeQ]]; tc=DivisorSigma[1, Select[Range[1000], !PrimeQ[ # ]&]]; Intersection[tp, tc]-1

CROSSREFS

Sequence in context: A160129 A145481 A006621 * A066938 A219602 A076812

Adjacent sequences:  A158910 A158911 A158912 * A158914 A158915 A158916

KEYWORD

nonn

AUTHOR

T. D. Noe, Mar 30 2009

STATUS

approved

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Last modified May 22 15:25 EDT 2013. Contains 225552 sequences.