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A295032 Numbers k such that 12*10^k - 7 is prime. 0
0, 1, 2, 4, 5, 8, 11, 21, 25, 105, 191, 305, 463, 704, 1320, 1404, 1580, 1675, 2215, 3475, 6323, 10560, 28817, 30356, 98198 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

For k > 1, numbers such that the digits 11 followed by k-1 occurrences of the digit 9 followed by the digit 3 is prime (see Example section).

a(26) > 10^5.

LINKS

Table of n, a(n) for n=1..25.

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

Makoto Kamada, Search for 119w3

EXAMPLE

2 is in this sequence because 12*10^2 - 7 = 1193 is prime.

Initial terms and primes associated:

a(1) = 0, 5;

a(2) = 1, 113;

a(3) = 2, 1193;

a(4) = 4, 119993;

a(5) = 5, 1199993; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[12*10^# - 7 ] &]

PROG

(PARI) isok(k) = isprime(12*10^k - 7); \\ Michel Marcus, Nov 13 2017

CROSSREFS

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

Sequence in context: A182564 A288523 A240179 * A280017 A080136 A080033

Adjacent sequences:  A295029 A295030 A295031 * A295033 A295034 A295035

KEYWORD

nonn,more,hard,changed

AUTHOR

Robert Price, Nov 12 2017

STATUS

approved

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Last modified January 18 23:05 EST 2019. Contains 319282 sequences. (Running on oeis4.)