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A102993 Numbers n such that 4*10^n + 5*R_n + 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
6, 21, 22, 24, 51, 81, 132, 165, 621, 1450, 3424, 5979, 11526, 26980, 49233, 84927 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Also numbers n such that (41*10^n+31)/9 is prime.

a(17) > 10^5. - Robert Price, May 25 2015

LINKS

Table of n, a(n) for n=1..16.

Makoto Kamada, Prime numbers of the form 455...559.

Index entries for primes involving repunits.

FORMULA

a(n) = A101728(n) + 1.

MATHEMATICA

Do[ If[ PrimeQ[(41*10^n + 31)/9], Print[n]], {n, 0, 10000}]

CROSSREFS

Cf. A002275, A101728.

Sequence in context: A302202 A200831 A184291 * A276803 A143416 A273787

Adjacent sequences:  A102990 A102991 A102992 * A102994 A102995 A102996

KEYWORD

more,nonn

AUTHOR

Robert G. Wilson v, Jan 17 2005

EXTENSIONS

Addition of a(13)-a(14) from Kamada data by Robert Price, Dec 12 2010

a(15) from Erik Branger, May 01 2013, submitted by Ray Chandler, Aug 16 2013

a(16) from Robert Price, May 25 2015

STATUS

approved

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Last modified September 19 11:06 EDT 2019. Contains 327192 sequences. (Running on oeis4.)