login
A295033
Numbers k such that (5*10^k + 79)/3 is prime.
0
1, 2, 3, 4, 5, 8, 9, 20, 291, 417, 712, 749, 1906, 2086, 2746, 3896, 4927, 10058, 18369, 34071, 36569, 44749, 89510, 139457
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 1 followed by k-2 occurrences of the digit 6 followed by the digits 93 is prime (see Example section).
a(25) > 2*10^5.
EXAMPLE
2 is in this sequence because (5*10^2 + 79)/3 = 193 is prime.
Initial terms and associated primes:
a(1) = 1, 43;
a(2) = 2, 193;
a(3) = 3, 1693;
a(4) = 4, 16693;
a(5) = 5, 166693; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(5*10^# + 79)/3] &]
PROG
(PARI) is(k) = ispseudoprime((5*10^k + 79)/3) \\ Iain Fox, Nov 12 2017
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Nov 12 2017
EXTENSIONS
a(24) from Robert Price, Mar 09 2018
STATUS
approved