

A257037


Numbers k such that 9*R_(k+2)  7*10^k is prime, where R_k = 11...1 is the repunit (A002275) of length n.


0



1, 8, 9, 14, 54, 80, 487, 551, 600, 2502, 2544, 5593, 7949, 8635, 13407, 31128, 45504, 45933, 52303, 65121, 167501, 359354
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OFFSET

1,2


COMMENTS

Also, numbers k such that 93*10^n1 is prime.
Terms from Kamada.
a(23) > 400000.


LINKS

Table of n, a(n) for n=1..22.
Makoto Kamada, Nearrepdigit numbers of the form ABAA...AA.
Makoto Kamada, Prime numbers of the form 9299...99.
Index entries for primes involving repunits.


EXAMPLE

For k=8, 9*R_10  7*10^8 = 9999999999  700000000 = 9299999999 which is prime.


MATHEMATICA

Select[Range[0, 400000], PrimeQ[93*10^#1 ] &]


PROG

(MAGMA) [n: n in [0..400]  IsPrime(93*10^n1)]; // Vincenzo Librandi, Apr 15 2015


CROSSREFS

Cf. A002275.
Sequence in context: A059869 A213016 A105833 * A114305 A101765 A256351
Adjacent sequences: A257034 A257035 A257036 * A257038 A257039 A257040


KEYWORD

more,hard,nonn


AUTHOR

Robert Price, Apr 14 2015


STATUS

approved



