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A294941 Numbers k such that (14*10^k + 211)/9 is prime. 0
2, 3, 5, 6, 8, 9, 18, 41, 209, 815, 2573, 3590, 4439, 4568, 6720, 16491, 20069, 22406, 36756, 43076, 53465, 58550, 70896, 74858, 184950 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For k > 1, numbers such that the digit 1 followed by k-2 occurrences of the digit 5 followed by the digits 79 is prime (see Example section).

a(26) > 2*10^5.

LINKS

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

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

Makoto Kamada, Search for 15w79

EXAMPLE

2 is in this sequence because (14*10^2 + 211)/9 = 179 s prime.

Initial terms and primes associated:

a(1) = 2, 179;

a(2) = 3, 1579;

a(3) = 5, 155579;

a(4) = 6, 1555579;

a(5) = 8, 155555579; etc.

MATHEMATICA

Select[Range[0 100000], PrimeQ[(14*10^# + 211)/9] &]

PROG

(PARI) isok(k) = isprime((14*10^k + 211)/9); \\ Michel Marcus, Nov 12 2017

CROSSREFS

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

Sequence in context: A063756 A117522 A299101 * A028374 A050578 A283513

Adjacent sequences:  A294938 A294939 A294940 * A294942 A294943 A294944

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Nov 11 2017

EXTENSIONS

a(25) from Robert Price, Apr 21 2018

STATUS

approved

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Last modified July 8 03:38 EDT 2020. Contains 335504 sequences. (Running on oeis4.)