A103099 Numbers n such that 9*10^n + 4*R_n + 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 2, 4, 25, 58, 148, 373, 421, 1915, 3746, 16784, 30050, 60026, 93346

Offset

1,2

Comments

Also numbers n such that (85*10^n+23)/9 is prime.

a(15) > 10^5. - Robert Price, Nov 14 2015

Links

Table of n, a(n) for n=1..14.

Makoto Kamada, Prime numbers of the form 944...447.

Index entries for primes involving repunits.

Formula

a(n) = A101008(n) + 1.

Mathematica

Do[ If[ PrimeQ[(85*10^n + 23)/9], Print[n]], {n, 0, 10000}]

Prog

(PARI) is(n)=isprime(9*10^n + 4*(10^n-1)/9 + 3) \\ Anders Hellström, Nov 14 2015

Crossrefs

Cf. A002275, A101008.

Sequence in context: A128299 A143672 A001510 * A342665 A266495 A365097

Adjacent sequences: A103096 A103097 A103098 * A103100 A103101 A103102

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 19 2005

Extensions

a(11) from Kamada data by Robert Price, Dec 14 2010

a(12) from Erik Branger May 01 2013 by Ray Chandler, Aug 17 2013

a(13)-a(14) from Robert Price, Nov 14 2015

Status

approved