A102939 Numbers k such that 10^k + 6*R_k - 3 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

1, 2, 3, 18, 177, 324, 388, 392, 404, 531, 1083, 12546, 22443, 54388, 72916, 185520

Offset

1,2

Comments

Also numbers k such that (5*10^k - 11)/3 is prime.

a(16) > 10^5. - Robert Price, Nov 15 2014

Links

Table of n, a(n) for n=1..16.

Makoto Kamada, Prime numbers of the form 166...663.

Index entries for primes involving repunits

Formula

a(n) = A102023(n) + 1.

Maple

A102939:=n->`if`(isprime((5*10^n-11)/3), n, NULL): seq(A102939(n), n=1..1000); # Wesley Ivan Hurt, Nov 15 2014

Mathematica

Do[ If[ PrimeQ[(5*10^n - 11)/3], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A102023.

Sequence in context: A076016 A226961 A107095 * A073983 A230602 A269343

Adjacent sequences: A102936 A102937 A102938 * A102940 A102941 A102942

Keyword

more,nonn

Author

Robert G. Wilson v, Dec 16 2004

Extensions

Addition of a(12)-a(13) from Kamada data by Robert Price, Dec 12 2010

a(14)-a(15) from Kamada data by Robert Price, Nov 15 2014

a(16) from Kamada data by Tyler Busby, Apr 16 2024

Status

approved