%I #14 Apr 06 2023 14:41:06

%S 3,5,6,10,11,17,20,24,26,29,30,38,41,46,51,55,59,71,85,88,101,105,107,

%T 114,118,126,135,136,137,141,145,147,149,155,158,161,177,178,179,185,

%U 191,197,203,206,207,209,216,227,230,236,238,239,255,269,278,281,296

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

%H Amiram Eldar, <a href="/A072282/b072282.txt">Table of n, a(n) for n = 1..10000</a>

%e sigma(20) + 1 = 43 and sigma(20) - 1 = 41, so 20 is a term of the sequence.

%t Select[Range[10^3], PrimeQ[DivisorSigma[1, # ] + 1] && PrimeQ[DivisorSigma[1, # ] - 1] &]

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

%o (PARI) isok(n) = my(p=sigma(n)-1); isprime(p) && isprime(p+2); \\ _Michel Marcus_, Sep 30 2019

%Y Cf. A000203, A068017.

%K easy,nonn

%O 1,1

%A _Joseph L. Pe_, Jul 10 2002

%E More terms from _Amiram Eldar_, Sep 30 2019