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A296094 Numbers k such that (43*10^k + 47)/9 is prime. 0
1, 3, 7, 12, 15, 21, 85, 177, 204, 477, 487, 1686, 2179, 2815, 2892, 3466, 7308, 17883, 25431, 69048, 89169, 126441 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For k > 1, numbers such that the digit 4 followed by k-2 occurrences of the digit 7 followed by the digits 83 is prime (see Example section).

a(23) > 2*10^5.

LINKS

Table of n, a(n) for n=1..22.

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

Makoto Kamada, Search for 47w83

EXAMPLE

3 is in this sequence because (43*10^3 + 47)/9 = 4783 is prime.

Initial terms and primes associated:

a(1) = 1, 53;

a(2) = 3, 4783;

a(3) = 7, 47777783;

a(4) = 12, 4777777777783;

a(5) = 15, 4777777777777783; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(43*10^# + 47)/9] &]

CROSSREFS

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

Sequence in context: A310234 A310235 A310236 * A075895 A033015 A225574

Adjacent sequences:  A296091 A296092 A296093 * A296095 A296096 A296097

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Dec 04 2017

EXTENSIONS

a(22) from Robert Price, Dec 01 2018

STATUS

approved

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Last modified December 10 20:23 EST 2019. Contains 329909 sequences. (Running on oeis4.)