OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 5 followed by k-2 occurrences of the digit 0 followed by the digits 87 is prime (see Example section).
a(34) > 2*10^5.
LINKS
Makoto Kamada, Search for 50w87.
EXAMPLE
3 is in this sequence because 5*10^3 + 87 = 5087 is prime.
Initial terms and associated primes:
a(1) = 1, 137;
a(2) = 2, 587;
a(3) = 3, 5087;
a(4) = 4, 50087;
a(5) = 6, 5000087, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[5*10^# + 87] &]
PROG
(PARI) is(n)=ispseudoprime(5*10^n + 87) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Apr 05 2016
EXTENSIONS
a(33) from Robert Price, Feb 24 2019
STATUS
approved