login
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
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.
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