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A068081 Numbers n such that n + phi(n) and n - phi(n) are prime. 1
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified October 27 15:27 EDT 2020. Contains 338035 sequences. (Running on oeis4.)