OFFSET
1,1
COMMENTS
For k > 3, numbers k such that k-4 occurrences of the digit 9 followed by the digits 1999 is prime (see Example section).
a(41) > 3*10^5.
LINKS
Makoto Kamada, Search for 9w1999.
EXAMPLE
4 is in this sequence because 10^4-8001 = 1999 is prime.
Initial terms and associated primes:
a(1) = 4, 1999;
a(2) = 6, 991999;
a(3) = 8, 99991999;
a(4) = 11, 99999991999;
a(5) = 12, 999999991999, etc.
MAPLE
isa := n -> isprime(10^n-8001):
select(isa, [$0..1000]); # Peter Luschny, Jul 22 2019
MATHEMATICA
Select[Range[0, 100000], PrimeQ[10^#-8001 && # > 3] &] (* Corrected by Georg Fischer, Jul 22 2019 *)
PROG
(PARI) isok(n) = isprime(10^n-8001); \\ Michel Marcus, Mar 18 2016
(PARI) lista(nn) = for(n=1, nn, if(ispseudoprime(10^n-8001), print1(n, ", "))); \\ Altug Alkan, Mar 18 2016
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Mar 17 2016
EXTENSIONS
a(36)-a(39) from Robert Price, Mar 27 2018
a(40) from Robert Price, May 31 2023
STATUS
approved