

A056654


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


507



0, 1, 2, 4, 8, 10, 23, 83, 220, 1313, 2951, 20015, 51053
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,3


COMMENTS

Also numbers k such that (10^(k+1)+17)/9 is prime.
a(14) > 10^5.  Robert Price, Nov 01 2014


LINKS

Table of n, a(n) for n=1..13.
Makoto Kamada, Prime numbers of the form 11...113.
Index entries for primes involving repunits


FORMULA

a(n) = A097683(n+1)  1.  Robert Price, Nov 01 2014


EXAMPLE

8 is a term because 111111113 is a prime.


MATHEMATICA

Do[ m = n; If[ primeQ[ 10*(10^n  1)/9 + 3 ], Print[ n ] ], {n, 1, 1350} ]


PROG

(PARI) is(n)=ispseudoprime(10^n\9*10+3) \\ Charles R Greathouse IV, Nov 10 2021


CROSSREFS

Cf. A093011 (corresponding primes), A097683.
Sequence in context: A127101 A308832 A124849 * A020950 A056386 A331027
Adjacent sequences: A056651 A056652 A056653 * A056655 A056656 A056657


KEYWORD

hard,nonn


AUTHOR

Robert G. Wilson v, Aug 09 2000


EXTENSIONS

a(11) (only a probable prime) from Rick L. Shepherd, Mar 14 2004
a(12)a(13) derived from A097683 by Robert Price, Nov 01 2014


STATUS

approved



