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A273042 Numbers k such that (28*10^k + 191)/3 is prime. 0
0, 1, 2, 3, 5, 6, 9, 10, 33, 49, 92, 109, 548, 757, 814, 1289, 1460, 1644, 2782, 6355, 8028, 9276, 9366, 9765, 12002, 12089, 14491, 16180, 29102, 30989, 151682, 183403, 190105 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

For k>1, numbers k such that the digit 9 followed by k-2 occurrences of the digit 3 followed by the digits 97 is prime (see Example section).

a(34) > 2*10^5.

LINKS

Table of n, a(n) for n=1..33.

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

Makoto Kamada, Search for 93w97.

EXAMPLE

3 is in this sequence because (28*10^3 + 191)/3 = 9397 is prime.

Initial terms and primes associated:

a(1) = 0, 73;

a(2) = 1, 157:

a(3) = 2, 997;

a(4) = 3, 9397;

a(5) = 5, 933397, etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(28*10^# + 191)/3] &]

PROG

(PARI) is(n)=ispseudoprime((28*10^n + 191)/3) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

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

Sequence in context: A018278 A137809 A219035 * A014838 A026459 A026461

Adjacent sequences:  A273039 A273040 A273041 * A273043 A273044 A273045

KEYWORD

nonn,more

AUTHOR

Robert Price, May 13 2016

EXTENSIONS

a(31)-a(33) from Robert Price, Feb 27 2020

STATUS

approved

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Last modified August 1 03:52 EDT 2021. Contains 346384 sequences. (Running on oeis4.)