

A099413


Numbers n such that 4*R_n + 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n.


2



0, 1, 2, 4, 10, 20, 26, 722, 1310, 3170, 28934, 66284, 67796
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OFFSET

1,3


COMMENTS

Also numbers n such that (4*10^n+23)/9 is prime.
a(14) > 10^5.  Robert Price, Nov 26 2014


LINKS

Table of n, a(n) for n=1..13.
Makoto Kamada, Prime numbers of the form 44...447.
Index entries for primes involving repunits


FORMULA

a(n) = A056682(n1) + 1.  Robert Price, Nov 26 2014


MATHEMATICA

Do[ If[ PrimeQ[ 4(10^n  1)/9 + 3], Print[n]], {n, 5000}]


CROSSREFS

Cf. A002275, A056682.
Sequence in context: A083844 A026554 A259132 * A271624 A283090 A283143
Adjacent sequences: A099410 A099411 A099412 * A099414 A099415 A099416


KEYWORD

nonn,hard,more


AUTHOR

Robert G. Wilson v, Oct 14 2004


EXTENSIONS

a(11)a(13) from Robert Price, Nov 26 2014


STATUS

approved



