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A056654 Numbers n such that 10*R_n + 3 is prime, where R_n is the repunit (A002275) of length n. 506
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 n such that (10^(n+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} ]

CROSSREFS

Cf. A093011 (corresponding primes), A097683.

Sequence in context: A004655 A127101 A124849 * A020950 A056386 A210108

Adjacent sequences:  A056651 A056652 A056653 * A056655 A056656 A056657

KEYWORD

hard,nonn,changed

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

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Last modified January 18 04:47 EST 2019. Contains 319269 sequences. (Running on oeis4.)