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A282139 Numbers k such that (22*10^k - 19)/3 is prime. 0
1, 2, 4, 6, 14, 15, 24, 48, 78, 112, 122, 334, 504, 872, 914, 1230, 1506, 2442, 4095, 5022, 10615, 11460, 18303, 33675, 47701, 55592, 84159 (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 3 followed by the digits 27 is prime (see Example section).

a(28) > 10^5.

LINKS

Table of n, a(n) for n=1..27.

Makoto Kamada, Factorization of near-repdigit-related numbers.

Makoto Kamada, Search for 73w27.

EXAMPLE

4 is in this sequence because (22*10^4 - 19)/3 = 73327 is prime.

Initial terms and primes associated:

a(1) = 1, 67;

a(2) = 2, 727;

a(3) = 4, 73327;

a(4) = 6, 7333327;

a(5) = 14, 733333333333327; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(22 * 10^# - 19)/3] &]

CROSSREFS

Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.

Sequence in context: A105543 A295618 A027712 * A138307 A124693 A095698

Adjacent sequences:  A282136 A282137 A282138 * A282140 A282141 A282142

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Feb 06 2017

STATUS

approved

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Last modified November 12 21:10 EST 2018. Contains 317116 sequences. (Running on oeis4.)