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A282506 Numbers k such that (5*10^k - 101)/3 is prime. 0
4, 19, 29, 42, 48, 57, 70, 71, 72, 124, 189, 216, 1860, 4170, 6132, 9226, 9725, 9906, 9942, 15283, 19386 (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 6 followed by the digits 33 is prime (see Example section).

a(22) > 10^5.

LINKS

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

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

Makoto Kamada, Search for 16w33.

EXAMPLE

4 is in this sequence because (5*10^4 - 101)/3 = 16633 is prime.

Initial terms and primes associated:

a(1) = 4, 16633;

a(2) = 19, 16666666666666666633;

a(3) = 29, 166666666666666666666666666633;

a(4) = 42, 1666666666666666666666666666666666666666633;

a(5) = 48, 1666666666666666666666666666666666666666666666633; etc.

MATHEMATICA

Select[Range[2, 100000], PrimeQ[(5*10^# - 101)/3] &]

CROSSREFS

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

Sequence in context: A022135 A192193 A028564 * A003338 A047715 A031291

Adjacent sequences:  A282503 A282504 A282505 * A282507 A282508 A282509

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Feb 16 2017

STATUS

approved

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Last modified February 23 13:19 EST 2018. Contains 299581 sequences. (Running on oeis4.)