A103013 Numbers n such that 5*10^n + 4*R_n - 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

0, 2, 3, 86, 134, 185, 344, 396, 476, 834, 1799, 2147, 2418, 5216, 5882, 6216, 13394, 19746, 66485

Offset

1,2

Comments

Also numbers n such that (49*10^n-31)/9 is prime.

a(20) > 10^5. - Robert Price, Jul 16 2015

Links

Table of n, a(n) for n=1..19.

Makoto Kamada, Prime numbers of the form 544...441.

Index entries for primes involving repunits.

Formula

a(n) = A101578(n-1) + 1, for n>1.

Mathematica

Do[ If[ PrimeQ[(49*10^n - 31)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101578.

Sequence in context: A242370 A153228 A041401 * A246121 A356798 A356788

Adjacent sequences: A103010 A103011 A103012 * A103014 A103015 A103016

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 18 2005

Extensions

a(17)-a(18) from Kamada data by Robert Price, Dec 14 2010

a(1) = 0 prepended by Robert Price, Jul 16 2015

a(19) from Robert Price, Jul 16 2015

Status

approved