login
A293396
Numbers k such that (13*10^k + 347)/9 is prime.
0
1, 3, 6, 9, 12, 18, 24, 31, 36, 39, 57, 91, 129, 529, 798, 1279, 1728, 6603, 12883, 29463, 77811
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 1 followed by k-2 occurrences of the digit 4 followed by the digits 83 is prime (see Example section).
a(22) > 2*10^5.
EXAMPLE
3 is in this sequence because (13*10^3 + 347)/9 = 1483 is prime.
Initial terms and associated primes:
a(1) = 1, 53;
a(2) = 3, 1483;
a(3) = 6, 1444483;
a(4) = 9, 1444444483;
a(5) = 12, 1444444444483; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(13*10^# + 347)/9] &]
PROG
(PARI) isok(k) = isprime((13*10^k + 347)/9); \\ Altug Alkan, Oct 08 2017
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Oct 08 2017
STATUS
approved