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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For k>1, numbers such that the digit 7 followed by k-2 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 near-repdigit-related 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

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Last modified September 19 11:06 EDT 2019. Contains 327192 sequences. (Running on oeis4.)