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A295627 Numbers k such that (397*10^k + 53)/9 is prime. 0
5, 9, 17, 47, 54, 75, 191, 207, 267, 894, 2099, 7164, 8625, 10865, 20394, 22251, 23088, 29015, 92369 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For k > 1, numbers such that the digits 44 followed by k-1 occurrences of the digit 1 followed by the digit 7 is prime (see Example section).

a(20) > 2*10^5.

LINKS

Table of n, a(n) for n=1..19.

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

Makoto Kamada, Search for 441w7.

EXAMPLE

5 is in this sequence because (397*10^5 + 531)/9 = 4411117 is prime.

Initial terms and primes associated:

a(1) = 5, 4411117;

a(2) = 9, 44111111117;

a(3) = 17, 4411111111111111117; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(397*10^# + 53)/9] &]

CROSSREFS

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

Sequence in context: A099213 A146067 A336139 * A300128 A334993 A262484

Adjacent sequences:  A295624 A295625 A295626 * A295628 A295629 A295630

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Nov 24 2017

STATUS

approved

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Last modified September 22 09:27 EDT 2021. Contains 347606 sequences. (Running on oeis4.)