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A102985 Numbers n such that 4*10^n + 2*R_n + 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
0, 1, 4, 9, 10, 31, 70, 160, 171, 277, 630, 724, 3717, 5542, 5634, 10656, 12724, 31954 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
COMMENTS
Also numbers n such that (38*10^n+7)/9 is prime.
a(19) > 10^5. - Robert Price, May 09 2015
LINKS
FORMULA
a(n) = A101720(n-1) + 1.
MATHEMATICA
Do[ If[ PrimeQ[(38*10^n + 7)/9], Print[n]], {n, 0, 10000}]
CROSSREFS
Sequence in context: A141395 A121215 A178224 * A112401 A178360 A197125
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Jan 17 2005
EXTENSIONS
Addition of a(16)-a(17) from Kamada data by Robert Price, Dec 12 2010
a(18) from Erik Branger, May 01 2013, submitted by Ray Chandler, Aug 16 2013
STATUS
approved

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Last modified May 25 06:49 EDT 2024. Contains 372782 sequences. (Running on oeis4.)