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A108327 Integers n such that 10^n-21 is a prime number. 3
2, 6, 32, 108, 408, 1286, 2268, 2328, 4284, 53558, 181182, 249010 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(13) > 2.5*10^5. - Robert Price, Apr 12 2015

LINKS

Table of n, a(n) for n=1..12.

Makoto Kamada, Near-repdigit numbers of the form AA...AABA.

Makoto Kamada, Prime numbers of the form 99...9979.

Index entries for primes involving repunits.

EXAMPLE

6 is a member because 10^6-21 = 1000000-21 = 999979, which is prime.

CROSSREFS

Cf. A089675, A095714, A092767.

Sequence in context: A109243 A223586 A212762 * A188573 A196010 A121071

Adjacent sequences:  A108324 A108325 A108326 * A108328 A108329 A108330

KEYWORD

more,nonn

AUTHOR

Julien Peter Benney (jpbenney(AT)ftml.net), Jun 30 2005

EXTENSIONS

Edited by Ray Chandler, Dec 23 2010

a(10)=53558 from Robert Price, Mar 03 2011

a(11)-a(12) from Kamada data by Robert Price, Apr 12 2015

STATUS

approved

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Last modified September 26 05:09 EDT 2017. Contains 292502 sequences.