A103068 Numbers n such that 8*10^n - 9 is prime.

1, 5, 11, 12, 17, 28, 46, 48, 61, 73, 138, 178, 213, 405, 762, 1053, 1157, 1427, 2865, 3148, 3615, 13447, 48081

Offset

1,2

Comments

Also numbers n such that 7*10^n + 9*R_n - 8 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

a(24) > 2*10^5. - Robert Price, Dec 19 2015

Links

Table of n, a(n) for n=1..23.

Makoto Kamada, Prime numbers of the form 799...991.

Index entries for primes involving repunits.

Formula

a(n) = A101154(n) + 1.

Mathematica

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

Prog

(PARI) is(n)=ispseudoprime(8*10^n-9) \\ Charles R Greathouse IV, Jun 12 2017

Crossrefs

Cf. A002275, A101154.

Sequence in context: A102175 A139200 A102181 * A277136 A176821 A070369

Adjacent sequences: A103065 A103066 A103067 * A103069 A103070 A103071

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 19 2005

Extensions

a(22)-a(23) from Kamada data by Robert Price, Dec 14 2010

Status

approved