OFFSET
1,2
COMMENTS
Numbers k such that the digits 49 followed by k-1 occurrences of the digit 0 followed by the digit 1 is prime (see Example section).
a(29) > 10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 490w1.
EXAMPLE
4 is in this sequence because 49*10^4 + 1 = 490001 is prime.
Initial terms and associated primes:
a(1) = 1, 491;
a(2) = 4, 490001;
a(3) = 5, 4900001;
a(4) = 7, 490000001;
a(5) = 9, 49000000001, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[49*10^#+1] &]
PROG
(PARI) is(n)=ispseudoprime(49*10^n+1) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Apr 07 2016
STATUS
approved