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A274037
Numbers k such that 3*10^k - 49 is prime.
0
2, 5, 6, 10, 16, 29, 35, 82, 107, 170, 185, 204, 223, 226, 388, 512, 1586, 2137, 3182, 7325, 7346, 8143, 8746, 11322, 11497, 13279, 44681, 108624, 183872
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 51 is prime (see Example section).
a(31) > 2*10^5.
EXAMPLE
5 is in this sequence because 3*10^5-49 = 299951 is prime.
Initial terms and associated primes:
a(1) = 2, 251;
a(2) = 5, 299951;
a(3) = 6, 2999951;
a(4) = 10, 29999999951;
a(5) = 16, 29999999999999951, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[3*10^# - 49] &]
PROG
(PARI) is(n)=ispseudoprime(3*10^n - 49) \\ Charles R Greathouse IV, Jun 08 2016
KEYWORD
nonn,more
AUTHOR
Robert Price, Jun 07 2016
EXTENSIONS
a(28)-a(29) from Robert Price, Jul 29 2018
STATUS
approved