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A262937 Numbers k such that (28*10^k - 13) / 3 is prime. 0
0, 1, 2, 4, 5, 8, 10, 14, 17, 20, 33, 64, 80, 152, 158, 166, 194, 196, 198, 901, 971, 1289, 1595, 2921, 14390, 28781, 35840 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

For k>1, numbers such that the digit 9 followed by k-2 occurrences of the digit 3 followed by the digits 29 is prime (see Example section).

a(28) > 2*10^5.

LINKS

Table of n, a(n) for n=1..27.

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

Makoto Kamada, Search for 93w29.

EXAMPLE

2 is in this sequence because (28*10^2 - 13) / 3 = 929 is prime.

Initial terms and primes associated:

a(1) = 0, 5;

a(2) = 1, 89;

a(3) = 2, 929;

a(4) = 4, 93329;

a(5) = 5, 933329, etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(28*10^# - 13) / 3] &]

PROG

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

CROSSREFS

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

Sequence in context: A259711 A182195 A092265 * A249508 A163295 A101274

Adjacent sequences:  A262934 A262935 A262936 * A262938 A262939 A262940

KEYWORD

nonn,more

AUTHOR

Robert Price, Sep 23 2016

STATUS

approved

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Last modified November 28 13:18 EST 2020. Contains 338724 sequences. (Running on oeis4.)