OFFSET
1,3
COMMENTS
For k > 1, numbers k such that the digit 6 followed by k-2 occurrences of the digit 0 followed by the digits 91 is prime (see Example section).
a(34) > 3*10^5.
LINKS
Makoto Kamada, Search for 60w91.
EXAMPLE
3 is in this sequence because 6*10^3+91 = 6091 is prime.
Initial terms and associated primes:
a(1) = 0, 97;
a(2) = 1, 151;
a(3) = 2, 691;
a(4) = 3, 6091;
a(5) = 4, 60091, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[6*10^# + 91] &]
PROG
(PARI) is(n)=ispseudoprime(6*10^n + 91) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Apr 06 2016
EXTENSIONS
a(33) from Robert Price, May 21 2019
STATUS
approved