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A272717
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Numbers k such that (65*10^k + 691)/9 is prime.
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0
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1, 5, 7, 17, 35, 46, 56, 148, 187, 190, 256, 551, 553, 1033, 1751, 1976, 2696, 3116, 3364, 5353, 5893, 8063, 9548, 10640, 24655, 77992
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OFFSET
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1,2
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COMMENTS
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For k > 1, numbers k such that the digit 7 followed by k-2 occurrences of the digit 2 followed by the digits 99 is prime (see Example section).
a(27) > 10^5.
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LINKS
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EXAMPLE
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5 is in this sequence because (65*10^5+691)/9 = 722299 is prime.
Initial terms and associated primes:
a(1) = 1, 149;
a(2) = 5, 722299;
a(3) = 7, 72222299;
a(4) = 17, 722222222222222299;
a(5) = 35, 722222222222222222222222222222222299, etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(65*10^#+691)/9] &]
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PROG
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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STATUS
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approved
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