A103001 Numbers n such that 5*10^n - 9 is prime.

1, 2, 4, 7, 24, 172, 173, 218, 439, 2563, 2782, 2880, 3715, 4392, 10820, 14592, 25054, 27769, 40168, 180992, 193907

Offset

1,2

Comments

Also numbers n such that 4*10^n + 9*R_n - 8 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

a(22) > 2*10^5. - Robert Price, May 30 2015

Links

Table of n, a(n) for n=1..21.

Makoto Kamada, Prime numbers of the form 499...991.

Index entries for primes involving repunits.

Formula

a(n) = A101738(n) + 1.

Mathematica

Do[ If[ PrimeQ[5*10^n - 9], Print[n]], {n, 0, 10000}]

Prog

(PARI) is(n)=ispseudoprime(5*10^n-9) \\ Charles R Greathouse IV, Jun 06 2017

Crossrefs

Cf. A002275, A101738.

Sequence in context: A099387 A359095 A036440 * A343798 A222987 A222907

Adjacent sequences: A102998 A102999 A103000 * A103002 A103003 A103004

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 17 2005

Extensions

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008

Addition of a(17)-a(19) from Kamada data by Robert Price, Dec 10 2010

a(20)-a(21) from Robert Price, May 30 2015

Status

approved