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A280969 Numbers k such that 7*10^k - 17 is prime. 0
1, 2, 3, 11, 16, 33, 35, 37, 39, 42, 64, 94, 123, 136, 308, 309, 310, 357, 965, 1109, 2178, 8916, 9471, 18330, 62127 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For k>1, numbers such that the digit 6 followed by k-2 occurrences of the digit 9 followed by the digits 83 is prime (see Example section).

a(26) > 2*10^5.

LINKS

Table of n, a(n) for n=1..25.

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

Makoto Kamada, Search for 69w83.

EXAMPLE

3 is in this sequence because 7*10^3- 17 = 6983 is prime.

Initial terms and primes associated:

a(1) = 1, 53;

a(2) = 2, 683;

a(3) = 3, 6983;

a(4) = 11, 699999999983;

a(5) = 16, 69999999999999983; etc. #t Select[Range[1, 100000], PrimeQ[7*10^# - 17] &]

CROSSREFS

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

Sequence in context: A076514 A071012 A228520 * A091734 A038902 A019355

Adjacent sequences:  A280966 A280967 A280968 * A280970 A280971 A280972

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Jan 11 2017

EXTENSIONS

Comment corrected by Harvey P. Dale, Apr 10 2019

STATUS

approved

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Last modified August 17 16:54 EDT 2019. Contains 326059 sequences. (Running on oeis4.)