OFFSET
1,2
COMMENTS
Numbers k such that the digits 30 followed by k-1 occurrences of the digit 3 followed by the digit 7 is prime (see Example section).
a(34) > 3*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 303w7.
EXAMPLE
4 is in this sequence because (91*10^4+11)/3 = 303337 is prime.
Initial terms and associated primes:
a(1) = 1, 307;
a(2) = 2, 3037;
a(3) = 4, 303337;
a(4) = 6, 30333337;
a(5) = 12, 30333333333337, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(91*10^# + 11)/3] &]
PROG
(PARI) lista(nn) = for(n=1, nn, if(ispseudoprime((91*10^n + 11)/3), print1(n, ", "))); \\ Altug Alkan, Apr 14 2016
(Magma) [n: n in [1..300] |IsPrime((91*10^n + 11) div 3)]; // Vincenzo Librandi, Apr 15 2016
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Apr 14 2016
EXTENSIONS
a(31)-a(33) from Robert Price, Feb 15 2020
STATUS
approved