OFFSET
1,3
COMMENTS
For k > 1, numbers k such that the digits 22 followed by k-1 occurrences of the digit 0 followed by the digit 7 is prime (see Example section).
a(36) > 3*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 220w7.
EXAMPLE
2 is in this sequence because 22*10^2+7 = 227 is prime.
Initial terms and associated primes:
a(1) = 0, 29;
a(2) = 1, 227;
a(3) = 2, 2207;
a(4) = 9, 22000000007;
a(5) = 13, 220000000000007, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[22*10^# + 7] &]
PROG
(PARI) is(n)=ispseudoprime(22*10^n + 7) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Apr 11 2016
EXTENSIONS
a(34)-a(35) from Robert Price, Jun 01 2023
STATUS
approved