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A278695 Numbers n such that (38*10^n - 119) / 9 is prime. 0
1, 2, 4, 5, 8, 14, 16, 17, 20, 22, 38, 134, 136, 152, 829, 1087, 2110, 3524, 4412, 7079, 10538, 17672, 21583, 24163, 35126, 72050 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For n>1, numbers such that the digit 4 followed by n-2 occurrences of the digit 2 followed by the digits 09 is prime (see Example section).

a(27) > 10^5.

LINKS

Table of n, a(n) for n=1..26.

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

Makoto Kamada, Search for 42w09.

EXAMPLE

4 is in this sequence because (38*10^4 - 119) / 9 = 42209 is prime.

Initial terms and primes associated:

a(1) = 1, 29;

a(2) = 2, 409;

a(3) = 4, 42209;

a(4) = 5, 422209;

a(5) = 8, 422222209; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(38*10^# - 119) / 9] &]

PROG

(PARI) isok(n) = isprime((38*10^n - 119) / 9); \\ Michel Marcus, Nov 27 2016

CROSSREFS

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

Sequence in context: A288668 A264800 A293189 * A105134 A226791 A184775

Adjacent sequences:  A278692 A278693 A278694 * A278696 A278697 A278698

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Nov 26 2016

STATUS

approved

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Last modified October 18 01:01 EDT 2018. Contains 316297 sequences. (Running on oeis4.)