

A282250


Numbers k such that 7*10^k + 79 is prime.


0



1, 3, 4, 5, 29, 40, 46, 64, 75, 235, 640, 654, 670, 719, 863, 1186, 1220, 1390, 1886, 2894, 2934, 3523, 3856, 4349, 4750, 16781, 22666, 37540, 38525, 41499, 73888, 81058, 115561
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OFFSET

1,2


COMMENTS

For k>1, numbers such that the digit 7 followed by k2 occurrences of the digit 0 followed by the digits 79 is prime (see Example section).
a(34) > 2*10^5.


LINKS

Table of n, a(n) for n=1..33.
Makoto Kamada, Factorization of nearrepdigitrelated numbers.
Makoto Kamada, Search for 70w79.


EXAMPLE

4 is in this sequence because 7*10^4 + 79 = 70079 is prime.
Initial terms and primes associated:
a(1) = 1, 149;
a(2) = 3, 7079;
a(3) = 4, 70079;
a(4) = 5, 700079;
a(5) = 29, 700000000000000000000000000079; etc.


MATHEMATICA

Select[Range[0, 100000], PrimeQ[7*10^# + 79] &]


CROSSREFS

Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
Sequence in context: A126896 A123957 A085285 * A254865 A085841 A163483
Adjacent sequences: A282247 A282248 A282249 * A282251 A282252 A282253


KEYWORD

nonn,more,hard


AUTHOR

Robert Price, Feb 09 2017


EXTENSIONS

a(33) from Robert Price, Jul 08 2019


STATUS

approved



