A102953 Numbers k such that 2*10^k + 4*R_k - 1 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
1, 4, 7, 12, 30, 94, 178, 196, 564, 1801, 3520, 3538, 8233, 35161, 37405, 42330, 70051, 90792, 124096, 152670
Offset: 1
Links
Programs
-
Mathematica
Do[ If[ PrimeQ[(22*10^n - 13)/9], Print[n]], {n, 0, 10000}]
Formula
a(n) = A101958(n) + 1.
Extensions
a(14)-a(16) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013
a(17)-a(18) from Robert Price, Mar 16 2015
a(19)-a(20) from Robert Price, Jun 11 2018
Comments