A102941 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, 3, 5, 7, 11, 12, 28, 36, 384, 629, 720, 1398, 2002, 2622, 6457, 19305, 38508, 46455, 95976, 102107, 148505, 189693

Offset

1,2

Comments

Also numbers k such that (5*10^k + 7)/3 is prime.

a(20) > 10^5. - Robert Price, Nov 15 2014

Links

Table of n, a(n) for n=1..22.

Makoto Kamada, Prime numbers of the form 166...669.

Index entries for primes involving repunits

Formula

a(n) = A102025(n) + 1.

Mathematica

Do[ If[ PrimeQ[(5*10^n + 7)/3], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A102025.

Sequence in context: A347465 A249370 A282810 * A114235 A285848 A086527

Adjacent sequences: A102938 A102939 A102940 * A102942 A102943 A102944

Keyword

more,nonn

Author

Robert G. Wilson v, Dec 16 2004

Extensions

Addition of a(16) from Kamada data by Robert Price, Dec 12 2010

a(17)-a(18) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

a(19) from Kamada data by Robert Price, Nov 15 2014

a(20)-a(22) from Kamada data by Tyler Busby, Apr 14 2024

Status

approved