A101394 Numbers k such that 4*10^k+9 is prime.

0, 2, 4, 5, 8, 9, 28, 191, 196, 2038, 34414, 39266, 50579, 94286, 108412, 130480, 178091, 185355

Offset: 1

Author

Julien Peter Benney (jpbenney(AT)ftml.net), Jan 15 2005

Keywords

• nonn

Comments

a(19) > 2*10^5. - Robert Price, May 24 2015

Examples

			n = 2, 4, 5, 8, 9 are members since 409, 40009, 400009, 400000009 and 4000000009 are all prime.
		

Links

• Makoto Kamada, Prime numbers of the form 400...009.
• Sabin Tabirca and Kieran Reynolds, Lacunary Prime Numbers.

Crossrefs

Cf. A088275, A056806, A101715.

Programs

Mathematica

Do[ If[ PrimeQ[4*10^n + 9], Print[n]], {n, 0, 10000}]

PARI

is(n)=ispseudoprime(4*10^n+9) \\ Charles R Greathouse IV, Jun 12 2017

Formula

a(n) = A101715(n-1) + 1.

Extensions

a(10)=2038 from Joao da Silva (zxawyh66(AT)yahoo.com), Sep 30 2005

a(11)-a(12) from Kamada data by Robert Price, Dec 13 2010

Edited by Ray Chandler, Dec 23 2010

a(13)-a(18) from Robert Price, May 24 2015