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A295826
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Numbers k such that (202*10^k - 13)/9 is prime.
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0
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1, 2, 4, 20, 22, 34, 35, 41, 185, 547, 644, 713, 1489, 1885, 3211, 3257, 3625, 6733, 47732, 165569, 172940, 195383
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OFFSET
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1,2
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COMMENTS
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For k > 0, numbers such that the digits 22 followed by k-1 occurrences of the digit 4 followed by the digit 3 is prime (see Example section).
a(23) > 2*10^5.
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LINKS
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EXAMPLE
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2 is in this sequence because (202*10^2 - 13)/9 = 2243 is prime.
Initial terms and primes associated:
a(1) = 1, 223;
a(2) = 2, 2243;
a(3) = 4, 224443;
a(4) = 20, 2244444444444444444443;
a(5) = 22, 224444444444444444444443; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(202*10^# - 13)/9] &]
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CROSSREFS
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KEYWORD
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nonn,more,hard
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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