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A271618
Numbers k such that 10^k - 801 is prime.
0
3, 4, 6, 14, 15, 16, 20, 46, 52, 114, 165, 468, 504, 568, 713, 748, 899, 958, 992, 1043, 1348, 2388, 3182, 4102, 8847, 10899, 11908, 18852, 25214, 40151, 40290, 51207, 71910, 166324
OFFSET
1,1
COMMENTS
For k > 2, numbers k such that k-3 occurrences of the digit 9 followed by the digits 199 is prime (see Example section).
a(35) > 2*10^5.
EXAMPLE
6 is in this sequence because 10^6-801 = 999199 is prime.
Initial terms and associated primes:
a(1) = 3, 199;
a(2) = 4, 9199;
a(3) = 6, 999199;
a(4) = 14, 99999999999199;
a(5) = 15, 999999999999199, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[10^#-801] &]
PROG
(PARI) is(n)=ispseudoprime(10^n-801) \\ Charles R Greathouse IV, Jun 13 2017
KEYWORD
nonn,more
AUTHOR
Robert Price, Apr 11 2016
EXTENSIONS
a(34) from Robert Price, Feb 14 2018
STATUS
approved