A099017 Numbers k such that 4*10^k + 6*R_k + 1 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

0, 1, 2, 6, 10, 12, 13, 22, 32, 46, 61, 68, 90, 110, 652, 1608, 1904, 2003, 3038, 3086, 9580, 9698, 10639, 14461

Offset

1,3

Comments

Also numbers k such that (14*10^k + 1)/3 is prime.

a(25) > 2*10^5. - Robert Price, Jul 11 2015

Links

Table of n, a(n) for n=1..24.

Makoto Kamada, Prime numbers of the form 466...667.

Index entries for primes involving repunits.

Formula

a(n) = A101731(n-1) + 1, for n>1.

Example

n = 1, 2, 6 are members since 47, 467, 4666667 are primes.

Mathematica

Do[ If[ PrimeQ[(14*10^n + 1)/3], Print[n]], {n, 0, 10000}] (* Robert G. Wilson v, Jan 17 2005 *)

Crossrefs

Cf. A002275, A099005, A098959, A101731.

Sequence in context: A085258 A133520 A346299 * A298748 A139799 A214586

Adjacent sequences: A099014 A099015 A099016 * A099018 A099019 A099020

Keyword

more,nonn

Author

Julien Peter Benney (jpbenney(AT)ftml.net), Nov 13 2004

Extensions

a(15)-a(22) from Robert G. Wilson v, Jan 17 2005

a(23)-a(24) from Kamada data by Robert Price, Dec 08 2010

Prepended a(1)=0 by Robert Price, Jul 11 2015

Status

approved