

A270613


Numbers k such that (68*10^k + 7)/3 is prime.


500



1, 2, 3, 4, 7, 10, 24, 25, 29, 34, 35, 37, 46, 49, 88, 103, 290, 381, 484, 696, 751, 886, 999, 1750, 5062, 6214, 9740, 12558, 16551, 24674, 28600, 37427, 48032, 61991, 70148, 72516, 99441, 179656
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OFFSET

1,2


COMMENTS

Numbers such that the digits 22 followed by k1 occurrences of the digit 6 followed by the digit 9 is prime (see Example section).
a(39) > 2*10^5.


LINKS

Table of n, a(n) for n=1..38.
Makoto Kamada, Search for 226w9.


EXAMPLE

3 is in this sequence because (68*10^3+7)/3 = 22669 is prime.
Initial terms and primes associated:
a(1) = 1, 229;
a(2) = 2, 2269;
a(3) = 3, 22669;
a(4) = 4, 226669;
a(5) = 7, 226666669, etc.


MATHEMATICA

Select[Range[0, 100000], PrimeQ[(68*10^# + 7)/3] &]


PROG

(PARI) lista(nn) = for(n=1, nn, if(ispseudoprime((68*10^n + 7)/3), print1(n, ", "))); \\ Altug Alkan, Mar 20 2016


CROSSREFS

Cf. A056654, A268448, A269303, A270339.
Sequence in context: A094863 A094862 A104722 * A296446 A226387 A102282
Adjacent sequences: A270610 A270611 A270612 * A270614 A270615 A270616


KEYWORD

nonn,more


AUTHOR

Robert Price, Mar 20 2016


EXTENSIONS

a(38) from Robert Price, Jan 16 2020


STATUS

approved



