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A293538
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Numbers k such that (8*10^k + 43)/3 is prime.
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0
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0, 1, 2, 4, 5, 10, 20, 34, 43, 70, 85, 138, 205, 574, 1378, 1512, 1770, 2434, 3073, 3330, 29443, 76840, 122203, 142932, 176908
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OFFSET
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1,3
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COMMENTS
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For k>1, numbers such that the digit 2 followed by k-2 occurrences of the digit 6 followed by the digits 81 is prime (see Example section).
a(26) > 2*10^5.
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LINKS
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EXAMPLE
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2 is in this sequence because (8*10^2 + 43)/3 = 281 is prime.
Initial terms and primes associated:
a(1) = 0, 17;
a(2) = 1, 41;
a(3) = 2, 281;
a(4) = 4, 26681;
a(5) = 5, 266681; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(8*10^# + 43)/3] &]
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PROG
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(PARI) lista(nn) = for(n=0, nn, if(isprime((8*10^n + 43)/3), print1(n, ", "))) \\ Iain Fox, Oct 18 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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EXTENSIONS
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STATUS
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approved
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