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A102993
Numbers n such that 4*10^n + 5*R_n + 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
1
6, 21, 22, 24, 51, 81, 132, 165, 621, 1450, 3424, 5979, 11526, 26980, 49233, 84927
OFFSET
1,1
COMMENTS
Also numbers n such that (41*10^n+31)/9 is prime.
a(17) > 10^5. - Robert Price, May 25 2015
FORMULA
a(n) = A101728(n) + 1.
MATHEMATICA
Do[ If[ PrimeQ[(41*10^n + 31)/9], Print[n]], {n, 0, 10000}]
CROSSREFS
Sequence in context: A302202 A200831 A184291 * A276803 A143416 A273787
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Jan 17 2005
EXTENSIONS
Addition of a(13)-a(14) from Kamada data by Robert Price, Dec 12 2010
a(15) from Erik Branger, May 01 2013, submitted by Ray Chandler, Aug 16 2013
a(16) from Robert Price, May 25 2015
STATUS
approved