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A098930 Numbers n such that 2*10^n + 5*R_n - 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
2, 3, 5, 6, 12, 186, 435, 1746, 3447, 18798, 70209 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Also numbers n such that (23*10^n-41)/9 is prime.

a(12) > 10^5. - Robert Price, Mar 04 2015

LINKS

Table of n, a(n) for n=1..11.

Makoto Kamada, Prime numbers of the form 255...551.

Index entries for primes involving repunits.

FORMULA

a(n) = A101961(n) + 1.

EXAMPLE

If n = 3 we get 2551, which is prime.

MATHEMATICA

Do[ If[ PrimeQ[(23*10^n - 41)/9], Print[n]], {n, 0, 10000}]

CROSSREFS

Cf. A002275, A101961.

Sequence in context: A125877 A118787 A191783 * A075372 A064725 A301761

Adjacent sequences:  A098927 A098928 A098929 * A098931 A098932 A098933

KEYWORD

more,nonn

AUTHOR

Julien Peter Benney (jpbenney(AT)ftml.net), Oct 20 2004

EXTENSIONS

a(7) from Ray Chandler, Nov 04 2004

a(8) & a(9) from Robert G. Wilson v, Dec 17 2004

Addition of a(10) from Kamada data by Robert Price, Dec 13 2010

a(11) from Robert Price, Mar 04 2015

STATUS

approved

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Last modified January 27 09:01 EST 2020. Contains 331293 sequences. (Running on oeis4.)