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A290433
Numbers k such that (85*10^k - 103)/9 is prime.
0
1, 3, 4, 16, 28, 45, 46, 67, 93, 130, 265, 321, 376, 717, 934, 1047, 1420, 2547, 5683, 8593, 9445, 31086, 33382, 43089, 76021, 90745
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 9 followed by k-2 occurrences of the digit 4 followed by the digits 33 is prime (see Example section).
a(27) > 2*10^5.
EXAMPLE
3 is in this sequence because (85*10^3 - 103)/9 = 9433 is prime.
Initial terms and associated primes:
a(1) = 1, 83;
a(2) = 3, 9433;
a(3) = 4, 94433;
a(4) = 16, 94444444444444433;
a(5) = 28, 94444444444444444444444444433; etc.
MATHEMATICA
Select[Range[1, 100000], PrimeQ[85*10^# - 103)/9] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Oct 06 2017
STATUS
approved