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A271548 Numbers k such that 4*10^k + 19 is prime. 0
0, 1, 2, 3, 9, 11, 19, 27, 31, 36, 42, 69, 86, 98, 152, 205, 533, 587, 1302, 1506, 1521, 1573, 1807, 3906, 6461, 9081, 11766, 12595, 15697, 17154, 30507, 36074, 52667, 61367, 122377, 169759 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

For k>1, numbers such that the digit 4 followed by k-2 occurrences of the digit 0 followed by the digits 19 is prime (see Example section).

a(37) > 2*10^5.

LINKS

Table of n, a(n) for n=1..36.

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

Makoto Kamada, Search for 40w19.

EXAMPLE

3 is in this sequence because 4*10^3 + 19 = 4019 is prime.

Initial terms and primes associated:

a(1) = 0, 23;

a(2) = 1, 59;

a(3) = 2, 419;

a(4) = 3, 4019;

a(5) = 9, 4000000019, etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[4*10^# + 19] &]

PROG

(PARI) is(n)=ispseudoprime(4*10^n + 19) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

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

Sequence in context: A111319 A109658 A257027 * A110350 A057569 A177950

Adjacent sequences:  A271545 A271546 A271547 * A271549 A271550 A271551

KEYWORD

nonn,more

AUTHOR

Robert Price, Apr 09 2016

EXTENSIONS

a(35)-a(36) from Robert Price, Oct 22 2018

STATUS

approved

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Last modified June 16 12:29 EDT 2021. Contains 345057 sequences. (Running on oeis4.)