A068081 Numbers n such that n + phi(n) and n - phi(n) are prime.

15, 33, 35, 51, 65, 77, 91, 95, 143, 161, 177, 209, 213, 215, 217, 247, 255, 303, 335, 341, 371, 411, 427, 435, 447, 455, 533, 545, 561, 573, 591, 611, 665, 707, 713, 717, 779, 803, 871, 917, 933, 965, 1001, 1041, 1067, 1105, 1115, 1133, 1157, 1159, 1211

Offset

1,1

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Maple

with(numtheory): for n from 1 by 2 to 10^4 do if [isprime(n+phi(n)),
isprime(n-phi(n))]=[true, true] then print(n); fi; od; # Muniru A Asiru, Aug 31 2017

Mathematica

Select[ Range[1500], PrimeQ[ # + EulerPhi[ # ]] && PrimeQ[ # - EulerPhi[ # ]] & ]
epQ[n_]:=Module[{ep=EulerPhi[n]}, AllTrue[n+{ep, -ep}, PrimeQ]]; Select[ Range[ 1500], epQ] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Aug 22 2016 *)

Prog

(PARI) is(n)=my(t=eulerphi(n)); isprime(n-t) && isprime(n+t) \\ Charles R Greathouse IV, Jan 25 2017
(GAP)
A068081:=[];; for n in [1, 3..10^4+1] do if IsPrime(n+Phi(n)) and IsPrime(n-Phi(n)) then Add(A068081, n); fi; od; A068081;  # Muniru A Asiru, Aug 31 2017

Crossrefs

Cf. A050530, A068080.

Sequence in context: A050384 A142862 A053343 * A089967 A064900 A277254

Adjacent sequences: A068078 A068079 A068080 * A068082 A068083 A068084

Keyword

easy,nonn

Author

Amarnath Murthy, Feb 17 2002

Extensions

Edited and extended by Robert G. Wilson v, Feb 18 2002

Status

approved