A109889 Numbers k such that 3^k - phi(k) is prime.

1, 4, 5, 6, 20, 22, 25, 46, 47, 214, 822, 985, 3273, 3590, 4658, 4768, 17250, 38697

Offset

1,2

Comments

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

a(19) > 10^5. - 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

Cf. A000010 (phi), A109887.

Sequence in context: A010753 A221174 A047195 * A103518 A103313 A036492

Adjacent sequences: A109886 A109887 A109888 * A109890 A109891 A109892

Keyword

nonn,hard,more

Author

Ryan Propper, Aug 31 2005

Extensions

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

Status

approved