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A270613
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Numbers k such that (68*10^k + 7)/3 is prime.
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500
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1, 2, 3, 4, 7, 10, 24, 25, 29, 34, 35, 37, 46, 49, 88, 103, 290, 381, 484, 696, 751, 886, 999, 1750, 5062, 6214, 9740, 12558, 16551, 24674, 28600, 37427, 48032, 61991, 70148, 72516, 99441, 179656
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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 22 followed by k-1 occurrences of the digit 6 followed by the digit 9 is prime (see Example section).
a(39) > 3*10^5.
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LINKS
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EXAMPLE
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3 is in this sequence because (68*10^3+7)/3 = 22669 is prime.
Initial terms and primes associated:
a(1) = 1, 229;
a(2) = 2, 2269;
a(3) = 3, 22669;
a(4) = 4, 226669;
a(5) = 7, 226666669, etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(68*10^# + 7)/3] &]
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PROG
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(PARI) lista(nn) = for(n=1, nn, if(ispseudoprime((68*10^n + 7)/3), print1(n, ", "))); \\ Altug Alkan, Mar 20 2016
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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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EXTENSIONS
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STATUS
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approved
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