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A280558 Numbers k such that (13*10^k + 89) / 3 is prime. 0
1, 2, 3, 6, 10, 12, 18, 34, 42, 61, 76, 85, 94, 178, 348, 451, 1123, 1455, 2234, 4519, 7502, 16036, 24216, 156522 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For k>1, numbers such that the digit 4 followed by k-2 occurrences of the digit 3 followed by the digits 63 is prime (see Example section).

a(25) > 2*10^5.

LINKS

Table of n, a(n) for n=1..24.

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

Makoto Kamada, Search for 43w63.

EXAMPLE

3 is in this sequence because (13*10^3 + 89) / 3 = 4363 is prime.

Initial terms and primes associated:

a(1) = 1, 73;

a(2) = 2, 463;

a(3) = 3, 4363;

a(4) = 6, 4333363;

a(5) = 10, 43333333363; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(13*10^# + 89) / 3] &]

PROG

(PARI) is(n)=ispseudoprime((13*10^n + 89)/3) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

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

Sequence in context: A038775 A065029 A239212 * A216920 A120754 A023547

Adjacent sequences:  A280555 A280556 A280557 * A280559 A280560 A280561

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Jan 05 2017

EXTENSIONS

a(24) from Robert Price, Sep 10 2018

STATUS

approved

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Last modified October 22 09:31 EDT 2019. Contains 328315 sequences. (Running on oeis4.)