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A295967 Numbers k such that (35*10^k - 377)/9 is prime. 0
2, 3, 6, 24, 33, 86, 335, 711, 1103, 1169, 1181, 2163, 3026, 7940, 8174, 9365, 10127, 13466, 40130, 70130, 174704, 198294 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For k > 1, numbers such that the digit 3 followed by k-2 occurrences of the digit 8 followed by the digits 47 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 38w47

EXAMPLE

2 is in this sequence because (35*10^2 - 377)/9 = 347 is prime.

Initial terms and primes associated:

a(1) = 2, 347;

a(2) = 3, 3847;

a(3) = 6, 3888847;

a(4) = 24, 3888888888888888888888847;

a(5) = 33, 3888888888888888888888888888888847; etc.

MATHEMATICA

Select[Range[2, 100000], PrimeQ[(35*10^# - 377)/9] &]

PROG

(PARI) isok(k) = isprime((35*10^k - 377)/9); \\ Michel Marcus, Dec 01 2017

CROSSREFS

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

Sequence in context: A018300 A317973 A171708 * A027163 A160683 A099000

Adjacent sequences:  A295964 A295965 A295966 * A295968 A295969 A295970

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Nov 30 2017

EXTENSIONS

a(21)-a(22) from Robert Price, Jul 19 2018

STATUS

approved

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Last modified October 21 07:01 EDT 2019. Contains 328292 sequences. (Running on oeis4.)