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

Author

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

Keywords

• more
• nonn

Comments

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

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

Examples

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

Links

• Makoto Kamada, Prime numbers of the form 466...667.
• Index entries for primes involving repunits.

Crossrefs

Cf. A002275, A099005, A098959, A101731.

Programs

Mathematica

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

Formula

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

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