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A271506 Numbers k such that (7*10^k + 179)/3 is prime. 0
1, 2, 3, 7, 8, 36, 41, 46, 74, 76, 88, 103, 115, 188, 194, 257, 310, 399, 511, 515, 776, 1134, 1404, 6545, 6569, 17600, 22209, 24397, 24842, 46957 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For k>1, numbers such that the digit 2 followed by k-2 occurrences of the digit 3 followed by the digits 93 is prime (see Example section).

a(34) > 2*10^5.

LINKS

Table of n, a(n) for n=1..30.

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

Makoto Kamada, Search for 23w93.

EXAMPLE

3 is in this sequence because (7*10^3 + 179)/3 = 2393 is prime.

Initial terms and primes associated:

a(1) = 1, 83;

a(2) = 2, 293;

a(3) = 3, 2393;

a(4) = 7, 23333393;

a(5) = 8, 233333393. etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(7*10^# + 179)/3] &]

PROG

(PARI) is(n)=ispseudoprime((7*10^n+179)/3) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

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

Sequence in context: A112994 A056036 A056432 * A056433 A288628 A064669

Adjacent sequences:  A271503 A271504 A271505 * A271507 A271508 A271509

KEYWORD

nonn,more

AUTHOR

Robert Price, Apr 08 2016

EXTENSIONS

a(31)-a(33) from Robert Price, Sep 01 2018

STATUS

approved

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Last modified October 23 13:15 EDT 2018. Contains 316528 sequences. (Running on oeis4.)