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A281407
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Numbers k such that (292*10^k - 1)/3 is prime.
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0
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0, 2, 4, 9, 14, 20, 28, 33, 156, 285, 302, 1121, 1300, 2540, 3873, 4706, 5297, 7292, 11086, 15928, 16203, 17267, 17793, 19326, 32009, 67659
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OFFSET
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1,2
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COMMENTS
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Numbers such that the digits 97 followed by k occurrences of the digit 3 is prime (see Example section).
a(27) > 2*10^5.
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LINKS
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EXAMPLE
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2 is in this sequence because (292*10^2 - 1)/3 = 9733 is prime.
Initial terms and primes associated:
a(1) = 0, 97;
a(2) = 2, 9733;
a(3) = 4, 973333;
a(4) = 9, 97333333333;
a(5) = 14, 9733333333333333; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(292*10^# - 1)/3] &]
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PROG
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(PARI) isok(n) = isprime((292*10^n - 1)/3); \\ Michel Marcus, Jan 21 2017
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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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STATUS
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approved
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