

A056704


Numbers k such that 3*10^k + 1*R_k is prime, where R_k = 11...1 is the repunit (A002275) of length k.


1



0, 1, 2, 5, 10, 11, 13, 34, 47, 52, 77, 88, 554, 580, 1310, 1505, 8537, 15892, 24022, 27041, 37922, 40033, 134122, 165358, 183760
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OFFSET

1,3


COMMENTS

Also numbers k such that (28*10^k  1)/9 is prime.
Although perhaps a degenerate case, A002275 defines R(0)=0. Thus zero belongs in this sequence since 3*10^0 + 0 = 3*1 + 0 = 3 is prime.  Robert Price, Oct 28 2014
a(26) > 2*10^5.  Robert Price, Dec 19 2014


LINKS

Table of n, a(n) for n=1..25.
Makoto Kamada, Prime numbers of the form 311...11.
Index entries for primes involving repunits


MATHEMATICA

Do[ If[ PrimeQ[ 3*10^n + (10^n1)/9], Print[n]], {n, 0, 10000}]


CROSSREFS

Cf. A002275, A068813.
Sequence in context: A136817 A140180 A175324 * A230408 A163624 A257031
Adjacent sequences: A056701 A056702 A056703 * A056705 A056706 A056707


KEYWORD

hard,nonn


AUTHOR

Robert G. Wilson v, Aug 10 2000


EXTENSIONS

Added zero by Robert Price, Oct 28 2014
a(18)a(25) from Kamada data by Robert Price, Dec 19 2014


STATUS

approved



