A103083 Numbers n such that 8*10^n + 5*R_n - 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

21, 27, 60, 471, 1074, 5781

Offset

1,1

Comments

Also numbers n such that (77*10^n-41)/9 is prime.

a(7) > 10^5. - Robert Price, Oct 21 2015

It appears that all terms are divisible by 3. - Robert Price, Oct 21 2015

Links

Table of n, a(n) for n=1..6.

Makoto Kamada, Prime numbers of the form 855...551.

Index entries for primes involving repunits.

Formula

a(n) = A101070(n) + 1.

Mathematica

Do[ If[ PrimeQ[(77*10^n - 41)/9], Print[n]], {n, 0, 10000}]

Prog

(PARI) for(n=1, 1e4, if(isprime((77*10^n-41)/9), print1(n, ", "))) \\ Altug Alkan, Oct 21 2015

Crossrefs

Cf. A002275, A101070.

Sequence in context: A098768 A208157 A114168 * A120735 A009727 A337702

Adjacent sequences: A103080 A103081 A103082 * A103084 A103085 A103086

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 19 2005

Status

approved