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A290577
Numbers k such that 3*10^k - 97 is prime.
0
3, 5, 6, 7, 28, 42, 45, 59, 69, 179, 271, 293, 621, 851, 2632, 2764, 5811, 6813, 7974, 17015, 30449, 32760, 43939, 85227, 87573, 93179, 122345, 156435, 174665, 177373, 292344
OFFSET
1,1
COMMENTS
For k > 1, numbers k such that the digit 2 followed by k-2 occurrences of the digit 9 followed by the digits 03 is prime (see Example section).
a(32) > 3*10^5.
EXAMPLE
5 is in this sequence because 3*10^5 - 97 = 299903 is prime.
Initial terms and associated primes:
a(1) = 3, 2903;
a(2) = 5, 299903;
a(3) = 6, 2999903;
a(4) = 7; 29999903;
a(5) = 28, 29999999999999999999999999903; etc.
MATHEMATICA
Select[Range[2, 100000], PrimeQ[3*10^# - 97] &]
PROG
(PARI) isok(n) = isprime(3*10^n - 97); \\ Michel Marcus, Aug 07 2017
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Aug 06 2017
EXTENSIONS
a(27)-a(30) from Robert Price, Jul 18 2018
a(31) from Robert Price, Jun 17 2023
STATUS
approved