OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 7 followed by k-2 occurrences of the digit 0 followed by the digits 43 is prime (see Example section).
a(29) > 10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 70w43.
EXAMPLE
3 is in this sequence because 7*10^3 + 43 = 7043 is prime.
Initial terms and associated primes:
a(1) = 1, 113;
a(2) = 2, 743;
a(3) = 3, 7043;
a(4) = 7, 70000043;
a(5) = 26, 700000000000000000000000043, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[7*10^# + 43] &]
PROG
(PARI) lista(nn) = for(n=1, nn, if(ispseudoprime(7*10^n + 43), print1(n, ", "))); \\ Altug Alkan, Jul 02 2016
(Magma) [n: n in [1..400] | IsPrime(7*10^n + 43)]; // Vincenzo Librandi, Jul 03 2016
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Jul 02 2016
STATUS
approved