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A271821
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Numbers n such that (5*10^n-143)/3 is prime.
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0
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3, 4, 5, 6, 10, 23, 30, 33, 64, 189, 207, 213, 463, 547, 1225, 1795, 3726, 3947, 4989, 5226, 9825, 11489, 12666, 14512, 19588, 28795, 29903, 31889, 71357
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OFFSET
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1,1
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COMMENTS
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For n>1, numbers such that the digit 1 followed by n-2 occurrences of the digit 6 followed by the digits 19 is prime (see Example section).
a(31) > 2*10^5.
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LINKS
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EXAMPLE
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4 is in this sequence because (5*10^4-143)/3 = 16619 is prime.
Initial terms and primes associated:
a(1) = 3, 1619;
a(2) = 4, 16619;
a(3) = 5, 166619;
a(4) = 6, 1666619;
a(5) = 10, 16666666619, etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(5*10^#-143)/3] &]
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PROG
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(PARI) lista(nn) = for(n=1, nn, if(ispseudoprime((5*10^n-143)/3), print1(n, ", "))); \\ Altug Alkan, Apr 14 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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STATUS
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approved
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