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A102957 Numbers n such that 2*10^n + 6*R_n + 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 2
0, 1, 2, 4, 7, 14, 20, 39, 102, 156, 457, 1190, 2308, 5870, 8314, 9703, 12828, 14959, 17995, 19730, 26480, 31440 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Also numbers n such that (8*10^n+7)/3 is prime.

LINKS

Table of n, a(n) for n=1..22.

Makoto Kamada, Prime numbers of the form 266...669.

Index entries for primes involving repunits.

FORMULA

a(n) = A101965(n-1) + 1.

MATHEMATICA

Do[ If[ PrimeQ[(8*10^n + 7)/3], Print[n]], {n, 0, 10000}]

CROSSREFS

Cf. A002275, A101965.

Sequence in context: A108329 A057264 A045514 * A216898 A176450 A263345

Adjacent sequences:  A102954 A102955 A102956 * A102958 A102959 A102960

KEYWORD

more,nonn

AUTHOR

Robert G. Wilson v, Dec 17 2004

EXTENSIONS

Addition of a(17)-a(21) from Kamada data by Robert Price, Dec 10 2010

0 added by Arkadiusz Wesolowski, Mar 10 2011

a(22) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

STATUS

approved

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Last modified March 25 10:23 EDT 2019. Contains 321470 sequences. (Running on oeis4.)