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A280925 Numbers k such that (29*10^k + 19)/3 is prime. 0
1, 13, 25, 29, 33, 46, 57, 61, 129, 187, 676, 779, 828, 1621, 1666, 1693, 2237, 2249, 2872, 3993, 5148, 6190, 6457, 25019, 30358, 60100 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For k>1, numbers such that the digit 9 followed by k-2 occurrences of the digit 6 followed by the digits 73 is prime (see Example section).

a(27) > 2*10^5.

LINKS

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

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

Makoto Kamada, Search for 96w73.

EXAMPLE

13 is in this sequence because (29*10^13 + 19)/3 = 96666666666673 is prime.

Initial terms and primes associated:

a(1) = 1, 103;

a(2) = 13, 96666666666673;

a(3) = 25, 96666666666666666666666673;

a(4) = 29, 966666666666666666666666666673;

a(5) = 33, 9666666666666666666666666666666673; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(29*10^# + 19)/3] &]

CROSSREFS

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

Sequence in context: A335466 A186403 A032478 * A161603 A075033 A017533

Adjacent sequences:  A280922 A280923 A280924 * A280926 A280927 A280928

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Jan 10 2017

STATUS

approved

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Last modified August 13 02:09 EDT 2020. Contains 336441 sequences. (Running on oeis4.)