A103000 Numbers k such that 4*10^k + 8*R_k + 1 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

0, 3, 4, 6, 10, 12, 18, 40, 48, 96, 106, 114, 144, 364, 618, 1090, 11370, 59454, 196684

Offset

1,2

Comments

Also numbers k such that (44*10^k+1)/9 is prime.

a(20) > 2*10^5. - Robert Price, Mar 30 2015

Links

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

Makoto Kamada, Prime numbers of the form 488...889.

Index entries for primes involving repunits.

Formula

a(n) = A101737(n-1) + 1.

Mathematica

Do[ If[ PrimeQ[(44*10^n + 1)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101737.

Sequence in context: A309317 A249666 A113887 * A344516 A392178 A383387

Adjacent sequences: A102997 A102998 A102999 * A103001 A103002 A103003

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 17 2005

Extensions

a(16)-a(18) from Kamada data added by Robert Price, Dec 10 2010

0 added by Arkadiusz Wesolowski, Mar 10 2011

Status

approved