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A295128
Numbers k such that 3*10^k - 37 is prime.
0
2, 3, 11, 15, 28, 46, 63, 65, 104, 105, 143, 188, 1380, 1599, 3365, 3549, 4535, 9192, 11799, 14745, 45588, 101657
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 63 is prime (see Example section).
a(23) > 2*10^5.
EXAMPLE
2 is in this sequence because 3*10^2 - 37 = 263 is prime.
Initial terms and associated primes:
a(1) = 2, 263;
a(2) = 3, 2963;
a(3) = 11, 299999999963;
a(4) = 15, 2999999999999963;
a(5) = 28, 29999999999999999999999999963; etc.
MATHEMATICA
Select[Range[2, 100000], PrimeQ[3*10^# - 37] &]
PROG
(PARI) isok(k) = isprime(3*10^k - 37); \\ Michel Marcus, Nov 15 2017
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Nov 15 2017
EXTENSIONS
a(22) from Robert Price, Jul 07 2018
STATUS
approved