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A274331 Numbers k such that (148*10^k - 1)/3 is prime. 0
2, 3, 4, 5, 9, 27, 35, 44, 88, 104, 205, 290, 302, 381, 400, 686, 917, 1150, 2278, 2757, 3220, 3316, 7469, 9535, 21442, 46409, 103718, 123688, 147139 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers k such that the digits 49 followed by k occurrences of the digit 3 is prime (see Example section).

a(30) > 2*10^5.

LINKS

Table of n, a(n) for n=1..29.

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

Makoto Kamada, Search for 493w.

EXAMPLE

3 is in this sequence because (148*10^3-1)/3 = 233329 is prime.

Initial terms and primes associated:

a(1) = 2, 4933;

a(2) = 3, 49333;

a(3) = 4, 493333;

a(4) = 5, 4933333;

a(5) = 9, 49333333333, etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(148*10^# - 1)/3] &]

PROG

(PARI) is(n)=ispseudoprime((148*10^n - 1)/3) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

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

Sequence in context: A162374 A323289 A065885 * A177064 A092233 A115895

Adjacent sequences:  A274328 A274329 A274330 * A274332 A274333 A274334

KEYWORD

nonn,more

AUTHOR

Robert Price, Jun 18 2016

EXTENSIONS

a(27)-a(29) from Robert Price, Mar 18 2020

STATUS

approved

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Last modified April 19 17:46 EDT 2021. Contains 343117 sequences. (Running on oeis4.)