A273868 Numbers k such that 10^k - 9^(k+1) is prime.

25, 51, 91, 107, 145, 651, 1473, 2145, 5577, 12457

Offset

1,1

Comments

a(11) > 10^5.

Links

Table of n, a(n) for n=1..10.

Example

25 is a term since 10^25 - 9^26 = 3538918110773326701067759, which is a prime number.

Mathematica

Select[Range[21, 100000], PrimeQ[10^# - 9^(# + 1)] &]

Prog

(PARI) is(n)=ispseudoprime(10^n-9^(n+1)) \\ Charles R Greathouse IV, Jun 08 2016

Crossrefs

Cf. A093713, A082103, A093717, A093793, A096185, A093794, A093795, A096186, A271883.

Sequence in context: A042238 A042234 A042232 * A338079 A337630 A270693

Adjacent sequences: A273865 A273866 A273867 * A273869 A273870 A273871

Keyword

nonn,more

Author

Robert Price, Jun 01 2016

Status

approved