OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 7 followed by k-2 occurrences of the digit 9 followed by the digits 51 is prime (see Example section).
a(35) > 2*10^5.
LINKS
Makoto Kamada, Search for 79w51.
EXAMPLE
3 is in this sequence because 8*10^3 - 49 = 7951 is prime.
Initial terms and associated primes:
a(1) = 1, 31;
a(2) = 2, 751;
a(3) = 3, 7951;
a(4) = 8, 799999951;
a(6) = 24, 7999999999999999999999951, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[8*10^# - 49] &]
PROG
(PARI) is(n)=isprime(8*10^n - 49) \\ Charles R Greathouse IV, Feb 16 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Apr 03 2016
EXTENSIONS
a(34) from Robert Price, Aug 20 2019
STATUS
approved