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A109889 Numbers n such that 3^n - phi(n) is prime. 0
1, 4, 5, 6, 20, 22, 25, 46, 47, 214, 822, 985, 3273, 3590, 4658, 4768, 17250, 38697 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Terms less than 1000 correspond to certified primes. Next term is greater than 10000.

a(19) > 10^5. [From Donovan Johnson, Feb 06 2010]

LINKS

Table of n, a(n) for n=1..18.

MATHEMATICA

Do[If[PrimeQ[3^n - EulerPhi[n]], Print[n]], {n, 1, 10^4}]

CROSSREFS

Sequence in context: A010753 A221174 A047195 * A103518 A103313 A036492

Adjacent sequences:  A109886 A109887 A109888 * A109890 A109891 A109892

KEYWORD

hard,nonn

AUTHOR

Ryan Propper, Aug 31 2005

EXTENSIONS

a(17)-a(18) from Donovan Johnson, Feb 06 2010

STATUS

approved

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Last modified March 7 18:15 EST 2021. Contains 341909 sequences. (Running on oeis4.)