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A103032 Numbers n such that 6*10^n + 3*R_n - 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 2
1, 2, 4, 7, 18, 19, 23, 24, 34, 41, 56, 64, 84, 149, 272, 755, 1272, 2398, 2686, 4800, 5198, 6217, 8737, 12388, 12391, 19702, 42404 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Also numbers n such that (19*10^n-7)/3 is prime.

a(28) > 10^5. - Robert Price, Sep 10 2015

LINKS

Table of n, a(n) for n=1..27.

Makoto Kamada, Prime numbers of the form 633...331.

Index entries for primes involving repunits.

FORMULA

a(n) = A101525(n) + 1.

MATHEMATICA

Do[ If[ PrimeQ[(19*10^n - 7)/3], Print[n]], {n, 0, 10000}]

CROSSREFS

Cf. A002275, A101525.

Sequence in context: A076894 A047871 A290877 * A215649 A259351 A300913

Adjacent sequences:  A103029 A103030 A103031 * A103033 A103034 A103035

KEYWORD

more,nonn

AUTHOR

Robert G. Wilson v, Jan 18 2005

EXTENSIONS

Addition of a(24)-a(26) from Kamada data by Robert Price, Dec 09 2010

a(27) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

STATUS

approved

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Last modified May 16 11:20 EDT 2021. Contains 343942 sequences. (Running on oeis4.)