

A102991


Numbers n such that 4*10^n + 5*R_n  2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.


2



0, 1, 4, 7, 19, 34, 54, 78, 90, 213, 307, 702, 1456, 2139, 2214, 3066, 9300, 16440, 16894, 28575, 54051
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OFFSET

1,3


COMMENTS

Also numbers n such that (41*10^n23)/9 is prime.
a(22) > 10^5. Robert Price, May 08 2015


LINKS

Table of n, a(n) for n=1..21.
Makoto Kamada, Prime numbers of the form 455...553.
Index entries for primes involving repunits.


FORMULA

a(n) = A101726(n1) + 1.


MATHEMATICA

Do[ If[ PrimeQ[(41*10^n  23)/9], Print[n]], {n, 0, 10000}]


CROSSREFS

Cf. A002275, A101726.
Sequence in context: A006381 A318099 A274691 * A298350 A291596 A323655
Adjacent sequences: A102988 A102989 A102990 * A102992 A102993 A102994


KEYWORD

more,nonn


AUTHOR

Robert G. Wilson v, Jan 17 2005


EXTENSIONS

Addition of a(17)a(19) from Kamada data by Robert Price, Dec 10 2010
0 added by Arkadiusz Wesolowski, Mar 10 2011
A(21) from Robert Price, May 08 2015


STATUS

approved



