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A271269
Numbers k such that 8*10^k - 49 is prime.
490
1, 2, 3, 8, 24, 49, 57, 74, 104, 131, 144, 162, 182, 246, 302, 352, 557, 581, 589, 704, 939, 1181, 1937, 2157, 4463, 6013, 7266, 8504, 8691, 16129, 20108, 40677, 74234, 112018
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.
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
KEYWORD
nonn,more
AUTHOR
Robert Price, Apr 03 2016
EXTENSIONS
a(34) from Robert Price, Aug 20 2019
STATUS
approved