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A290150 Numbers k such that (316*10^k - 1)/9 is prime. 0
2, 3, 8, 9, 11, 14, 17, 23, 29, 38, 50, 129, 164, 578, 1592, 2951, 4505, 16826, 17438, 22748 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers such that the digits 35 followed by k occurrences of the digit 1 is prime (see Example section).

a(21) > 2*10^5.

LINKS

Table of n, a(n) for n=1..20.

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

Makoto Kamada, Search for 351w.

EXAMPLE

3 is in this sequence because (316*10^3 - 1)/9 = 35111 is prime.

Initial terms and primes associated:

a(1) = 2, 3511;

a(2) = 3, 35111;

a(3) = 8, 3511111111;

a(4) = 9, 35111111111;

a(5) = 11, 3511111111111; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(316*10^# - 1)/9] &]

CROSSREFS

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

Sequence in context: A028821 A337261 A288740 * A237037 A283618 A284370

Adjacent sequences:  A290147 A290148 A290149 * A290151 A290152 A290153

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Jul 21 2017

STATUS

approved

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Last modified May 27 01:35 EDT 2022. Contains 354092 sequences. (Running on oeis4.)