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A271269 Numbers k such that 8*10^k - 49 is prime. 490
1, 2, 3, 8, 24, 49, 57, 74, 104, 131, 144, 162, 182, 246, 302, 352, 557, 581, 589, 704, 939, 1181, 1937, 2157, 4463, 6013, 7266, 8504, 8691, 16129, 20108, 40677, 74234, 112018 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For k>1, numbers such that the digit 7 followed by k-2 occurrences of the digit 9 followed by the digits 51 is prime (see Example section).

a(35) > 2*10^5.

LINKS

Table of n, a(n) for n=1..34.

Makoto Kamada, Search for 79w51.

EXAMPLE

3 is in this sequence because 8*10^3 - 49 = 7951 is prime.

Initial terms and primes associated:

a(1) = 1, 31;

a(2) = 2, 751;

a(3) = 3, 7951;

a(4) = 8, 799999951;

a(6) = 24, 7999999999999999999999951, etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[8*10^# - 49] &]

PROG

(PARI) is(n)=isprime(8*10^n - 49) \\ Charles R Greathouse IV, Feb 16 2017

CROSSREFS

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

Sequence in context: A120763 A120708 A327009 * A089847 A304121 A038561

Adjacent sequences:  A271266 A271267 A271268 * A271270 A271271 A271272

KEYWORD

nonn,more

AUTHOR

Robert Price, Apr 03 2016

EXTENSIONS

a(34) from Robert Price, Aug 20 2019

STATUS

approved

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Last modified January 24 07:11 EST 2020. Contains 331189 sequences. (Running on oeis4.)