

A257039


Numbers k such that 9*R_(k+2)  4*10^k is prime, where R_k = 11...1 is the repunit (A002275) of length n.


0



10, 12, 63, 69, 156, 328, 340, 344, 444, 672, 894, 1464, 1670, 1708, 2010, 4306, 7888, 8864, 9478, 9621, 26004, 36992, 71600, 98738, 118949, 130565, 140326, 183452, 211983, 225618
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OFFSET

1,1


COMMENTS

Also, numbers k such that 96*10^n1 is prime.
Terms from Kamada.
846519 reported to Kamada by Bruno DallOsto is also in this sequence. It may or may not be a(31).
a(31) > 230000.


LINKS

Table of n, a(n) for n=1..30.
Makoto Kamada, Nearrepdigit numbers of the form ABAA...AA.
Makoto Kamada, Prime numbers of the form 9599...99.
Index entries for primes involving repunits.


EXAMPLE

For k=10, 9*R_12  4*10^10 = 999999999999  40000000000 = 959999999999 which is prime.


MATHEMATICA

Select[Range[0, 230000], PrimeQ[96*10^#1 ] &]


PROG

(MAGMA) [n: n in [0..400]  IsPrime(96*10^n1)]; // Vincenzo Librandi, Apr 15 2015


CROSSREFS

Cf. A002275.
Sequence in context: A266700 A242508 A219917 * A223150 A333258 A241252
Adjacent sequences: A257036 A257037 A257038 * A257040 A257041 A257042


KEYWORD

more,hard,nonn


AUTHOR

Robert Price, Apr 14 2015


STATUS

approved



