A072282 Numbers n such that sigma(n) + 1 and sigma(n) - 1 are twin primes.

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

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] &]
Select[Range[300], AllTrue[DivisorSigma[1, #]+{1, -1}, PrimeQ]&] (* Harvey P. Dale, Apr 06 2023 *)

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