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A294570 Numbers k such that (58*10^k + 329)/9 is prime. 0
0, 1, 3, 6, 19, 22, 27, 48, 70, 130, 364, 594, 603, 799, 2442, 3168, 5059, 5563, 6523, 12282, 13498, 34099, 86242, 122170, 161691 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

For k>1, numbers such that the digit 6 followed by k-2 occurrences of the digit 4 followed by the digits 81 is prime (see Example section).

a(26) > 2*10^5.

LINKS

Table of n, a(n) for n=1..25.

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

Makoto Kamada, Search for 64w81.

EXAMPLE

3 is in this sequence because (58*10^3 + 329)/9 = 6481 is prime.

Initial terms and primes associated:

a(1) = 0, 43;

a(2) = 1, 101;

a(3) = 3, 6481;

a(4) = 6, 6444481;

a(5) = 19, 64444444444444444481; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(58*10^# + 329)/9] &]

CROSSREFS

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

Sequence in context: A057268 A085401 A085061 * A306968 A090956 A108972

Adjacent sequences:  A294567 A294568 A294569 * A294571 A294572 A294573

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Nov 02 2017

EXTENSIONS

a(24)-a(25) from Robert Price, May 01 2019

STATUS

approved

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Last modified November 19 20:42 EST 2019. Contains 329323 sequences. (Running on oeis4.)