login
A281303
Numbers k such that (10^k + 77)/3 is prime.
0
1, 2, 3, 4, 5, 8, 16, 20, 56, 58, 75, 109, 124, 217, 221, 368, 439, 595, 1309, 6986, 11600, 20855, 29327, 34305, 42145, 44056, 52667, 75707, 79067, 81848, 119836, 164284, 176584
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that k-2 occurrences of the digit 3 followed by the digits 59 is prime (see Example section).
a(34) > 2*10^5.
EXAMPLE
3 is in this sequence because (10^3 + 77)/3 = 359 is prime.
Initial terms and associated primes:
a(1) = 1, 29;
a(2) = 2, 59;
a(3) = 3, 359;
a(4) = 4, 3359;
a(5) = 5, 33359; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(10^# + 77)/3] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Jan 21 2017
EXTENSIONS
a(31)-a(33) from Robert Price, Jan 18 2018
STATUS
approved