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A102953 Numbers n such that 2*10^n + 4*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 2
1, 4, 7, 12, 30, 94, 178, 196, 564, 1801, 3520, 3538, 8233, 35161, 37405, 42330, 70051, 90792, 124096, 152670 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Also numbers n such that (22*10^n-13)/9 is prime.

a(21) > 2*10^5. - Robert Price, Jun 11 2018

LINKS

Table of n, a(n) for n=1..20.

Makoto Kamada, Prime numbers of the form 244...443.

Index entries for primes involving repunits.

FORMULA

a(n) = A101958(n) + 1.

MATHEMATICA

Do[ If[ PrimeQ[(22*10^n - 13)/9], Print[n]], {n, 0, 10000}]

CROSSREFS

Cf. A002275, A101958.

Sequence in context: A215329 A208724 A183336 * A111157 A255340 A272251

Adjacent sequences:  A102950 A102951 A102952 * A102954 A102955 A102956

KEYWORD

more,nonn

AUTHOR

Robert G. Wilson v, Dec 17 2004

EXTENSIONS

a(14)-a(16) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

a(17)-a(18) from Robert Price, Mar 16 2015

a(19)-a(20) from Robert Price, Jun 11 2018

STATUS

approved

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Last modified March 22 17:25 EDT 2019. Contains 321422 sequences. (Running on oeis4.)