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A294377 Numbers k such that (19*10^k - 43)/3 is prime. 0
2, 21, 29, 40, 46, 58, 64, 84, 90, 96, 452, 530, 566, 1133, 4584, 9059, 11753, 21636, 23168, 38867, 56597, 56933, 63960, 66878, 75518, 82270, 83894, 84144, 108176, 122836, 143129 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For k>1, numbers such that the digit 6 followed by k-2 occurrences of the digit 3 followed by the digits 19 is prime (see Example section).

a(32) > 2*10^5.

LINKS

Table of n, a(n) for n=1..31.

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

Makoto Kamada, Search for 63w19.

EXAMPLE

2 is in this sequence because (19*10^2 - 43)/3 = 619 is prime.

Initial terms and primes associated:

a(1) = 2, 619;

a(2) = 21, 6333333333333333333319;

a(3) = 29, 633333333333333333333333333319;

a(4) = 40, 63333333333333333333333333333333333333319;

a(5) = 46, 63333333333333333333333333333333333333333333319; etc.

MATHEMATICA

Select[Range[1, 100000], PrimeQ[(19*10^# - 43)/3] &]

CROSSREFS

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

Sequence in context: A079907 A075715 A326735 * A071761 A101316 A006920

Adjacent sequences:  A294374 A294375 A294376 * A294378 A294379 A294380

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Oct 29 2017

EXTENSIONS

a(29)-a(31) from Robert Price, May 02 2019

STATUS

approved

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Last modified August 7 08:08 EDT 2020. Contains 336274 sequences. (Running on oeis4.)