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A098960 Numbers n such that 2*10^n + 7*R_n - 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
2, 6, 33, 69, 150, 936, 3135, 5838, 6990, 20786 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Also numbers n such that (25*10^n-61)/9 is prime.

LINKS

Table of n, a(n) for n=1..10.

Makoto Kamada, Factorizations of 277...771.

Index entries for primes involving repunits.

EXAMPLE

For n = 2 and 6, we get 271 and 2777771 which are primes.

MATHEMATICA

Do[ If[ PrimeQ[(25*10^n - 61)/9], Print[n]], {n, 0, 10000}]

CROSSREFS

Sequence in context: A213435 A083666 A083126 * A162429 A243324 A018952

Adjacent sequences:  A098957 A098958 A098959 * A098961 A098962 A098963

KEYWORD

more,nonn

AUTHOR

Julien Peter Benney (jpbenney(AT)ftml.net), Oct 22 2004

EXTENSIONS

a(6) from Ray Chandler, Nov 04 2004

a(7), a(8) & a(9) from Sam Handler (sam_5_5_5_0(AT)yahoo.com), Nov 03 2004

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

STATUS

approved

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Last modified November 28 09:09 EST 2014. Contains 250301 sequences.