A067890 Primes p such that phi(p+1) = phi(p-1).

5, 11, 71, 911, 1609, 2591, 4339, 15401, 58309, 59149, 80989, 208391, 215389, 496511, 589189, 1809079, 1970149, 3167569, 3260809, 3516109, 5914369, 9832271, 12231311, 13608071, 14470061, 16537151, 16692551, 19018369, 19462661

Offset

1,1

Comments

Primes in A066812.

Links

Giovanni Resta, Table of n, a(n) for n = 1..675

Formula

a(n) = prime(A066902(n)). - Giovanni Resta, Apr 06 2020

Mathematica

Select[Prime[Range[124*10^4]], EulerPhi[#-1]==EulerPhi[#+1]&] (* Harvey P. Dale, Apr 09 2019 *)

Prog

(PARI) v=[]; forprime(p=2, 40000000, if(eulerphi(p+1)==eulerphi(p-1), v=concat(v, p))); v

Crossrefs

Cf. A066902, A066812.

Sequence in context: A189802 A328453 A175207 * A303549 A192436 A154797

Adjacent sequences: A067887 A067888 A067889 * A067891 A067892 A067893

Keyword

easy,nonn

Author

Benoit Cloitre, Mar 02 2002

Extensions

More terms from Rick L. Shepherd, May 03 2002

Status

approved