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A294631 Numbers k such that (59*10^k - 77)/9 is prime. 0
2, 3, 5, 6, 9, 14, 21, 29, 30, 32, 39, 59, 69, 113, 410, 13484, 15525, 16796, 22064, 37694, 38103, 73217 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For k>1, numbers such that the digit 6 followed by k-2 occurrences of the digit 5 followed by the digits 47 is prime (see Example section).

a(23) > 10^5.

LINKS

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

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

Makoto Kamada, Search for 65w47

EXAMPLE

2 is in this sequence because (59*10^2 - 77)/9 = 647 is prime.

Initial terms and primes associated:

a(1) = 2, 647;

a(2) = 3, 6547;

a(3) = 5, 655547;

a(4) = 6, 6555547;

a(5) = 9, 6555555547; etc.

MATHEMATICA

Select[Range[1, 100000], PrimeQ[(59*10^# - 77)/9] &]

CROSSREFS

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

Sequence in context: A181902 A295631 A278707 * A059454 A138538 A240555

Adjacent sequences:  A294628 A294629 A294630 * A294632 A294633 A294634

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Nov 05 2017

STATUS

approved

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Last modified May 24 00:38 EDT 2019. Contains 323528 sequences. (Running on oeis4.)