A103054 Numbers k such that 7*10^k + 2*R_k + 7 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
1, 3, 4, 7, 9, 13, 33, 37, 76, 147, 297, 1851, 3457, 3609, 45219
Offset: 1
Links
Programs
-
Magma
[n: n in [0..3*10^2]| IsPrime((65*10^n+61) div 9)]; // Vincenzo Librandi, Oct 02 2015
-
Mathematica
Do[ If[ PrimeQ[(65*10^n + 61)/9], Print[n]], {n, 0, 10000}] Select[Range[10000], PrimeQ[(65 10^# + 61)/9] &] (* Vincenzo Librandi, Oct 02 2015 *) -
PARI
for(n=1, 1e4, if (isprime((65*10^n+61)/9), print1(n", "))) \\ Altug Alkan, Oct 02 2015
Formula
a(n) = A101136(n) + 1.
Extensions
a(15) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013
Comments