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A272717 Numbers n such that (65*10^n+691)/9 is prime. 0
1, 5, 7, 17, 35, 46, 56, 148, 187, 190, 256, 551, 553, 1033, 1751, 1976, 2696, 3116, 3364, 5353, 5893, 8063, 9548, 10640, 24655, 77992 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For n>1, numbers such that the digit 7 followed by n-2 occurrences of the digit 2 followed by the digits 99 is prime (see Example section).

a(27) > 10^5.

LINKS

Table of n, a(n) for n=1..26.

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

Makoto Kamada, Search for 72w99.

EXAMPLE

5 is in this sequence because (65*10^5+691)/9 = 722299 is prime.

Initial terms and primes associated:

a(1) = 1, 149;

a(2) = 5, 722299;

a(3) = 7, 72222299;

a(4) = 17, 722222222222222299;

a(5) = 35, 722222222222222222222222222222222299, etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(65*10^#+691)/9] &]

PROG

(PARI) is(n)=ispseudoprime((65*10^n+691)/9) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

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

Sequence in context: A290471 A261792 A166977 * A018538 A038968 A243400

Adjacent sequences:  A272714 A272715 A272716 * A272718 A272719 A272720

KEYWORD

nonn,more

AUTHOR

Robert Price, Aug 11 2016

STATUS

approved

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Last modified February 29 05:25 EST 2020. Contains 332353 sequences. (Running on oeis4.)