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A272537 Numbers k such that (28*10^k + 173)/3 is prime. 0
0, 1, 2, 3, 9, 11, 13, 15, 17, 24, 37, 44, 48, 58, 65, 104, 393, 413, 1265, 2292, 2620, 3037, 3628, 5159, 5629, 12809, 18572, 26875, 29695, 32267, 34277, 43621, 138768 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

For k>1, numbers n such that the digit 9 followed by k-2 occurrences of the digit 3 followed by the digits 91 is prime (see Example section).

a(34) > 2*10^5.

LINKS

Table of n, a(n) for n=1..33.

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

Makoto Kamada, Search for 93w91.

EXAMPLE

3 is in this sequence because (28*10^3 + 173)/3 = 9391 is prime.

Initial terms and primes associated:

a(1) = 0, 67;

a(2) = 1, 151;

a(3) = 2, 991;

a(4) = 3, 9391;

a(5) = 9, 9333333391, etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(28*10^# + 173)/3] &]

PROG

(PARI) is(n)=ispseudoprime((28*10^n + 173)/3) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

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

Sequence in context: A328970 A103039 A140222 * A121557 A138984 A110772

Adjacent sequences:  A272534 A272535 A272536 * A272538 A272539 A272540

KEYWORD

nonn,more

AUTHOR

Robert Price, May 02 2016

EXTENSIONS

a(33) from Robert Price, Dec 25 2019

STATUS

approved

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Last modified August 8 14:36 EDT 2020. Contains 336298 sequences. (Running on oeis4.)