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A275020 Numbers k such that (5*10^k + 91) / 3 is prime. 0
1, 2, 3, 10, 19, 35, 43, 80, 107, 143, 199, 218, 255, 304, 353, 560, 904, 996, 1051, 6141, 8075, 9913, 11151, 28469, 75244, 108960, 122592, 178206, 187471 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

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

a(30) > 2*10^5.

LINKS

Table of n, a(n) for n=1..29.

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

Makoto Kamada, Search for 16w97.

EXAMPLE

3 is in this sequence because (5*10^3 + 91) / 3 = 1697 is prime.

Initial terms and associated primes:

a(1) = 1, 47;

a(2) = 2, 197;

a(3) = 3, 1697;

a(4) = 10, 16666666697;

a(5) = 19, 16666666666666666697, etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(5*10^# + 91) / 3] &]

PROG

(PARI) is(n)=ispseudoprime((5*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: A215121 A329850 A175569 * A122822 A295951 A083944

Adjacent sequences:  A275017 A275018 A275019 * A275021 A275022 A275023

KEYWORD

nonn,more

AUTHOR

Robert Price, Nov 12 2016

EXTENSIONS

a(26)-a(29) from Robert Price, Apr 28 2018

STATUS

approved

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Last modified June 16 19:05 EDT 2021. Contains 345068 sequences. (Running on oeis4.)