

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
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OFFSET

1,2


COMMENTS

For k > 1, numbers such that the digit 4 followed by k2 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 nearrepdigitrelated 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



