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A282536 Numbers k such that (26*10^k + 49)/3 is prime. 0
1, 2, 5, 6, 18, 25, 34, 67, 73, 98, 287, 380, 544, 748, 911, 947, 978, 2480, 3017, 7951, 13081, 17665, 17798, 34857, 43960, 100566 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For k>1, numbers such that the digit 8 followed by k-2 occurrences of the digit 6 followed by the digits 83 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 86w83.

EXAMPLE

2 is in this sequence because (26*10^2 + 49)/3 = 883 is prime.

Initial terms and primes associated:

a(1) = 1, 103;

a(2) = 2, 883;

a(3) = 5, 866683;

a(4) = 6, 8666683;

a(5) = 18, 8666666666666666683; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(26*10^# + 49)/3] &]

PROG

(PARI) isok(k) = isprime((26*10^k + 49)/3); \\ Michel Marcus, Feb 18 2017

CROSSREFS

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

Sequence in context: A319756 A202854 A274911 * A248719 A184594 A014454

Adjacent sequences:  A282533 A282534 A282535 * A282537 A282538 A282539

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Feb 17 2017

EXTENSIONS

a(26) from Robert Price, Jul 31 2019

STATUS

approved

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Last modified November 20 10:09 EST 2019. Contains 329334 sequences. (Running on oeis4.)