

A056661


Numbers k such that 40*R_k + 3 is prime, where R_k = 11...1 is the repunit (A002275) of length k.


2



0, 1, 2, 5, 8, 11, 29, 31, 182, 296, 491, 41315
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OFFSET

1,3


COMMENTS

Also numbers k such that (4*10^(k+1)13)/9 is prime.
a(13) > 10^5.  Robert Price, Nov 01 2014


LINKS

Table of n, a(n) for n=1..12.
Makoto Kamada, Prime numbers of the form 44...443.
Index entries for primes involving repunits


FORMULA

a(n) = A096845(n)  1.  Robert Price, Nov 01 2014


MATHEMATICA

Do[ If[ PrimeQ[ 40*(10^n  1)/9 + 3], Print[n]], {n, 0, 5000}]


CROSSREFS

Cf. A002275, A096845.
Sequence in context: A264613 A285293 A246442 * A229883 A135050 A004112
Adjacent sequences: A056658 A056659 A056660 * A056662 A056663 A056664


KEYWORD

hard,more,nonn


AUTHOR

Robert G. Wilson v, Aug 09 2000


EXTENSIONS

a(12) derived from A096845 by Robert Price, Nov 01 2014


STATUS

approved



