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 57 is prime (see Example section).
a(35) > 2*10^5.
LINKS
Makoto Kamada, Search for 70w57.
EXAMPLE
3 is in this sequence because 7*10^3+57 = 7057 is prime.
Initial terms and associated primes:
a(1) = 1, 127;
a(2) = 2, 757;
a(3) = 3, 7057;
a(4) = 5, 700057;
a(5) = 6, 7000057;
a(6) = 7, 70000057, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[7*10^# + 57] &]
PROG
(PARI) lista(nn) = {for(n=1, nn, if(ispseudoprime(7*10^n + 57), print1(n, ", "))); } \\ Altug Alkan, Mar 27 2016
(Magma) [n: n in [1..500] | IsPrime(7*10^n + 57)]; // Vincenzo Librandi, Jul 03 2016
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Mar 27 2016
EXTENSIONS
a(35) from Robert Price, Jun 13 2019
STATUS
approved