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
Keywords
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.
Programs
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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
Comments