A101392 Numbers k such that 2*10^k+9 is prime.
0, 1, 5, 25, 455, 761, 9205, 13561, 15955, 26669, 113941
Offset: 1
Examples
n = 1, 5 are members since 29 and 200009 are primes.
Links
- Makoto Kamada, Prime numbers of the form 200...009.
- Sabin Tabirca and Kieran Reynolds, Lacunary Prime Numbers.
Programs
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Mathematica
Do[ If[ PrimeQ[2*10^n + 9], Print[n]], {n, 0, 10000}] -
PARI
is(n)=ispseudoprime(2*10^n+9) \\ Charles R Greathouse IV, Jun 12 2017
Formula
a(n) = A101952(n-1) + 1 for n>1.
Extensions
a(8)-a(9) from Kamada link by Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
a(10)-a(11) from Kamada data by Robert Price, Dec 13 2010
Prepended a(1)=0 by Robert Price, Jun 06 2015
Comments