OFFSET
1,2
COMMENTS
Numbers k such that the digits 22 followed by k-1 occurrences of the digit 6 followed by the digit 9 is prime (see Example section).
a(39) > 3*10^5.
LINKS
Makoto Kamada, Search for 226w9.
EXAMPLE
3 is in this sequence because (68*10^3+7)/3 = 22669 is prime.
Initial terms and associated primes:
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
KEYWORD
nonn,more
AUTHOR
Robert Price, Mar 20 2016
EXTENSIONS
a(38) from Robert Price, Jan 16 2020
STATUS
approved