OFFSET
1,2
COMMENTS
For k > 0, numbers k such that the digits 88 followed by k-1 occurrences of the digit 0 followed by the digit 7 is prime (see Example section).
a(28) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 880w7.
EXAMPLE
4 is in this sequence because 88*10^4 + 7 = 880007is prime.
Initial terms and associated primes:
a(1) = 1, 887;
a(2) = 2, 8807;
a(3) = 3, 88007;
a(4) = 4, 880007;
a(5) = 8, 8800000007, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[88*10^# + 7] &]
PROG
(PARI) is(n)=ispseudoprime(88*10^n + 7) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Nov 11 2016
EXTENSIONS
a(27) from Robert Price, Mar 17 2020
STATUS
approved