OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 2 followed by the digits 93 is prime (see Example section).
a(30) > 2*10^5.
LINKS
Makoto Kamada, Search for 42w93.
EXAMPLE
4 is in this sequence because (38*10^4+637)/9 = 42293 is prime.
Initial terms and associated primes:
a(1) = 1, 113;
a(2) = 4, 42293;
a(3) = 14, 422222222222293;
a(4) = 19, 42222222222222222293;
a(5) = 25, 42222222222222222222222293, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(38*10^# + 637)/9] &]
PROG
(PARI) lista(nn) = for(n=1, nn, if(ispseudoprime((38*10^n + 637)/9), print1(n, ", "))); \\ Altug Alkan, Apr 05 2016
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Apr 05 2016
STATUS
approved