OFFSET
1,2
COMMENTS
For k > 0, numbers k such that the digits 19 followed by k-1 occurrences of the digit 0 followed by the digit 1 is prime (see Example section).
a(26) > 10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 190w1.
EXAMPLE
3 is in this sequence because 19*10^3 + 1 = 19001 is prime.
Initial terms and associated primes:
a(1) = 1, 191;
a(2) = 2, 1901;
a(3) = 3, 19001;
a(4) = 11, 1900000000001;
a(5) = 18, 19000000000000000001, etc.
MAPLE
select(k->isprime(19*(10^k)+1), [$1..3000]); # Muniru A Asiru, Oct 07 2018
MATHEMATICA
Select[Range[0, 100000], PrimeQ[19*10^# + 1] &]
PROG
(PARI) is(n) = ispseudoprime(19*(10^n) + 1); \\ Altug Alkan, Jan 15 2016
(PARI) lista(nn) = for(n=1, nn, if(isprime(19*(10^n) +1 ), print1(n, ", "))); \\ Altug Alkan, Jan 18 2016
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Emre APARI, Jan 14 2016
EXTENSIONS
a(13)-a(20) from Altug Alkan, Jan 18 2016
a(21)-a(25) from Robert Price, Oct 07 2018
STATUS
approved