login
A102986
Numbers n such that 4*10^n + 2*R_n + 5 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
1
1, 4, 136, 181, 325, 3292, 3871, 4690, 7876, 11911, 16096, 21649, 43045
OFFSET
1,2
COMMENTS
Also numbers n such that (38*10^n+43)/9 is prime.
a(14) > 10^5. - Robert Price, May 08 2015
FORMULA
a(n) = A101721(n) + 1.
MATHEMATICA
Do[ If[ PrimeQ[(38*10^n + 43)/9], Print[n]], {n, 0, 10000}]
CROSSREFS
Sequence in context: A263588 A006429 A016483 * A012160 A012197 A202299
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Jan 17 2005
EXTENSIONS
Addition of a(10)-a(12) from Kamada data by Robert Price, Dec 13 2010
a(13) from Erik Branger, May 01 2013, submitted by Ray Chandler, Aug 16 2013
STATUS
approved