login
A102988
Numbers n such that 4*10^n + 3*R_n - 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
1
1, 2, 4, 7, 10, 12, 20, 24, 30, 42, 62, 188, 304, 340, 715, 804, 1040, 1887, 2079, 2120, 2260, 2423, 3319, 5598, 6072, 22048, 25713, 28644, 43353
OFFSET
1,2
COMMENTS
Also numbers n such that (13*10^n-7)/3 is prime.
a(30) > 10^5. - Robert Price, Mar 30 2015
FORMULA
a(n) = A101723(n) + 1.
MATHEMATICA
Do[ If[ PrimeQ[(13*10^n - 7)/3], Print[n]], {n, 1, 10000}]
CROSSREFS
Sequence in context: A007087 A101359 A007303 * A080137 A102933 A122019
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Jan 17 2005
EXTENSIONS
Addition of a(26)-a(28) from Kamada data by Robert Price, Dec 08 2010
a(29) from Erik Branger, May 01 2013, submitted by Ray Chandler, Aug 16 2013
STATUS
approved