OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 0 followed by the digits 87 is prime (see Example section).
a(33) > 3*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 40w87.
EXAMPLE
4 is in this sequence because 4*10^4 + 87 = 40087 is prime.
Initial terms and associated primes:
a(1) = 1, 127:
a(2) = 2, 487;
a(3) = 4, 40087;
a(4) = 5, 400087;
a(5) = 13, 40000000000087, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[4*10^# + 87] &]
PROG
(PARI) is(n)=ispseudoprime(4*10^n + 87) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, May 15 2016
EXTENSIONS
a(32) from Robert Price, Aug 15 2018
STATUS
approved