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 A072282 Numbers n such that sigma(n) + 1 and sigma(n) - 1 are twin primes. 2
 3, 5, 6, 10, 11, 17, 20, 24, 26, 29, 30, 38, 41, 46, 51, 55, 59, 71, 85, 88, 101, 105, 107, 114, 118, 126, 135, 136, 137, 141, 145, 147, 149, 155, 158, 161, 177, 178, 179, 185, 191, 197, 203, 206, 207, 209, 216, 227, 230, 236, 238, 239, 255, 269, 278, 281, 296 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Amiram Eldar, Table of n, a(n) for n = 1..10000 EXAMPLE sigma(20) + 1 = 43 and sigma(20) - 1 = 41, so 20 is a term of the sequence. MATHEMATICA Select[Range[10^3], PrimeQ[DivisorSigma[1, # ] + 1] && PrimeQ[DivisorSigma[1, # ] - 1] &] PROG (PARI) isok(n) = my(p=sigma(n)-1); isprime(p) && isprime(p+2); \\ Michel Marcus, Sep 30 2019 CROSSREFS Cf. A000203, A068017. Sequence in context: A187127 A187126 A065873 * A028727 A257346 A047327 Adjacent sequences:  A072279 A072280 A072281 * A072283 A072284 A072285 KEYWORD easy,nonn AUTHOR Joseph L. Pe, Jul 10 2002 EXTENSIONS More terms from Amiram Eldar, Sep 30 2019 STATUS approved

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Last modified February 24 22:04 EST 2020. Contains 332216 sequences. (Running on oeis4.)