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A278335
Numbers k such that 9*10^k + 89 is prime.
0
1, 4, 5, 7, 9, 15, 26, 43, 75, 106, 129, 141, 147, 171, 351, 512, 927, 1156, 2563, 2689, 3274, 4211, 5709, 6908, 11781, 14464, 31451, 34921, 36635, 38087, 55707, 59617, 104361, 123549
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 9 followed by k-2 occurrences of the digit 0 followed by the digits 89 is prime (see Example section).
a(35) > 2*10^5.
EXAMPLE
4 is in this sequence because 9*10^4 + 89 = 90089 is prime.
Initial terms and associated primes:
a(1) = 1, 179;
a(2) = 4, 90089;
a(3) = 5, 900089;
a(4) = 7, 90000089;
a(5) = 9, 9000000089; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[9*10^# + 89] &]
PROG
(PARI) is(n)=ispseudoprime(9*10^n + 89) \\ Charles R Greathouse IV, Jun 13 2017
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Nov 18 2016
EXTENSIONS
a(33)-a(34) from Robert Price, Nov 09 2019
STATUS
approved