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A293851 Numbers k such that (8*10^k - 83)/3 is prime. 0
2, 12, 18, 24, 42, 54, 250, 378, 472, 490, 722, 2722, 3109, 3296, 7342, 10507, 14206, 20088, 27542, 65507, 76220 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For k>1, numbers such that the digit 2 followed by k-2 occurrences of the digit 6 followed by the digits 39 is prime (see Example section).

a(22) > 2*10^5.

LINKS

Table of n, a(n) for n=1..21.

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

Makoto Kamada, Search for 26w39

EXAMPLE

2 is in this sequence because (8*10^2 - 83)/3 = 239 is prime.

Initial terms and primes associated:

a(1) =  2: 239;

a(2) = 12: 2666666666639;

a(3) = 18: 2666666666666666639;

a(4) = 24: 2666666666666666666666639;

a(5) = 42: 2666666666666666666666666666666666666666639; etc.

MATHEMATICA

Select[Range[2, 100000], PrimeQ[(8*10^# - 83)/3] &]

CROSSREFS

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

Sequence in context: A294998 A323762 A120350 * A032413 A262897 A281353

Adjacent sequences:  A293848 A293849 A293850 * A293852 A293853 A293854

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Oct 17 2017

STATUS

approved

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Last modified June 30 07:11 EDT 2022. Contains 354914 sequences. (Running on oeis4.)