A103070 Numbers n such that 8*10^n + 9 is prime.

0, 1, 2, 3, 6, 12, 20, 21, 37, 42, 55, 60, 98, 100, 104, 223, 237, 260, 501, 570, 600, 698, 8857, 20911, 24345, 31964, 67742, 162924

Offset

1,3

Comments

a(29) > 2*10^5. - Robert Price, Dec 18 2015

Links

Table of n, a(n) for n=1..28.

Makoto Kamada, Prime numbers of the form 800...009.

Sabin Tabirca and Kieran Reynolds, Lacunary Prime Numbers.

Index entries for primes involving repunits.

Formula

a(n) = A101057(n-1) + 1, for n>1.

Example

For n =0, 8*10^0 + 9 = 8 + 9 = 17, hence 0 is a term.

Mathematica

Do[ If[ PrimeQ[ 8*10^n + 9], Print[ n ]], {n, 0, 10000}]

Prog

(PARI) for(n=0, 1e3, if(ispseudoprime(8*10^n + 9), print1(n, ", "))) \\ Altug Alkan, Dec 18 2015
(Magma) [n: n in [0..3*10^2] | IsPrime(8*10^n + 9)]; // Vincenzo Librandi, Dec 20 2015

Crossrefs

Cf. A101057.

Sequence in context: A007335 A309311 A361693 * A233422 A361382 A079708

Adjacent sequences: A103067 A103068 A103069 * A103071 A103072 A103073

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 19 2005

Extensions

a(23)-a(26) from Kamada data by Robert Price, Dec 14 2010

a(1) = 0 inserted and a(28) added by Robert Price, Dec 18 2015

Status

approved