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A068081
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Numbers n such that n + phi(n) and n - phi(n) are prime.
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1
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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
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OFFSET
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1,1
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LINKS
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MAPLE
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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
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MATHEMATICA
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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 *)
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PROG
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(GAP)
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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