

A056721


Numbers n such that 8*10^n1 is prime.


4



0, 1, 4, 5, 8, 10, 25, 49, 76, 128, 175, 238, 550, 796, 1219, 2012, 2846, 11336, 21296, 49808, 74318, 236891, 608989
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OFFSET

1,3


COMMENTS

Also numbers n such that 7*10^n + 9*R_n is prime, where R_n = 11...1 is the repunit (A002275) of length n.


LINKS

Table of n, a(n) for n=1..23.
Makoto Kamada, Prime numbers of the form 799...99.
Index entries for primes involving repunits


MATHEMATICA

Do[ If[ PrimeQ[ 7*10^n + (10^n1)], Print[n]], {n, 0, 3000}]


PROG

(PARI) is(n)=ispseudoprime(8*10^n1) \\ Charles R Greathouse IV, Feb 20 2017


CROSSREFS

Sequence in context: A190394 A116050 A241413 * A057479 A050140 A190860
Adjacent sequences: A056718 A056719 A056720 * A056722 A056723 A056724


KEYWORD

hard,nonn,more


AUTHOR

Robert G. Wilson v, Aug 11 2000


EXTENSIONS

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(22)a(23) from Kamada data by Robert Price, Oct 19 2014


STATUS

approved



