login
A282351
Numbers k such that (13*10^k + 437)/9 is prime.
0
2, 3, 6, 14, 17, 29, 41, 44, 87, 213, 354, 840, 972, 1263, 2018, 2534, 4868, 7992, 13676, 18354, 19304, 40515, 126638, 135279
OFFSET
1,1
COMMENTS
For k > 1, numbers k such that the digit 1 followed by k-2 occurrences of the digit 4 followed by the digits 93 is prime (see Example section).
a(25) > 2*10^5.
EXAMPLE
3 is in this sequence because (13*10^3 + 437)/9 = 1493 is prime.
Initial terms and associated primes:
a(1) = 2, 193;
a(2) = 3, 1493;
a(3) = 6, 1444493;
a(4) = 14, 144444444444493;
a(5) = 17, 144444444444444493; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(13*10^# + 437)/9] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Feb 12 2017
EXTENSIONS
a(23)-a(24) from Robert Price, Apr 14 2018
STATUS
approved