OFFSET
1,1
LINKS
Giovanni Resta, Table of n, a(n) for n = 1..769 (terms < 10^12)
MATHEMATICA
fQ[p_] := DivisorSigma[1, p - 1] == DivisorSigma[1, p + 1]; p = 2; lst = {}; While[p < 100000000, If[fQ@ p, AppendTo[lst, p]]; p = NextPrime@ p]; lst (* Vladimir Joseph Stephan Orlovsky, Dec 03 2009 and modified by Robert G. Wilson v, May 08 2016 *)
PROG
(PARI) for(n=2, 10^8, if(isprime(n) && sigma(n+1)==sigma(n-1), print1(n, ", "))) \\ It is more efficient to use forprime(...).
(PARI) is_A067891(p)=sigma(p-1)==sigma(p+1)&&isprime(p) \\ M. F. Hasler, Jul 31 2015
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, Mar 02 2002
EXTENSIONS
More terms from Rick L. Shepherd, Apr 19 2002
STATUS
approved