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A271645 Numbers n such that (23*10^n+91)/3 is prime. 0
1, 2, 4, 15, 16, 19, 20, 26, 38, 47, 52, 75, 122, 191, 246, 257, 294, 305, 374, 592, 682, 729, 1092, 2053, 2997, 4065, 13936, 17214, 19059, 37433 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For n>1, numbers such that the digit 7 followed by n-2 occurrences of the digit 6 followed by the digits 97 is prime (see Example section).

a(31) > 10^5.

LINKS

Table of n, a(n) for n=1..30.

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

Makoto Kamada, Search for 76w97.

EXAMPLE

4 is in this sequence because (23*10^4+91)/3 = 76697 is prime.

Initial terms and primes associated:

a(1) = 1, 107;

a(2) = 2, 797;

a(3) = 4, 76697;

a(4) = 15, 7666666666666697;

a(5) = 16, 76666666666666697, etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(23*10^#+91)/3] &]

PROG

(PARI) is(n)=ispseudoprime((23*10^n+91)/3) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

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

Sequence in context: A196239 A019543 A304568 * A265483 A154906 A260299

Adjacent sequences:  A271642 A271643 A271644 * A271646 A271647 A271648

KEYWORD

nonn,more

AUTHOR

Robert Price, Apr 11 2016

STATUS

approved

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Last modified April 25 23:48 EDT 2019. Contains 322465 sequences. (Running on oeis4.)