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A102954
Numbers n such that 2*10^n + 4*R_n + 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
1
3, 9, 15, 21, 27, 87, 180, 1941, 3960, 4995, 8577, 23481, 27855, 80595
OFFSET
1,1
COMMENTS
Also numbers n such that (22*10^n+23)/9 is prime.
a(15) > 10^5. - Robert Price, Mar 15 2015
FORMULA
a(n) = A101959(n) + 1.
MATHEMATICA
Do[ If[ PrimeQ[(22*10^n + 23)/9], Print[n]], {n, 0, 10000}]
CROSSREFS
Sequence in context: A222640 A110108 A162843 * A272749 A273560 A246388
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Dec 17 2004
EXTENSIONS
Addition of a(12)-a(13) from Kamada data by Robert Price, Dec 12 2010
a(14) from Robert Price, Mar 15 2015
STATUS
approved