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A295392
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Numbers k such that 5*10^k + 57 is prime.
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0
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1, 2, 5, 8, 14, 23, 24, 26, 41, 62, 85, 137, 209, 446, 1424, 1783, 3301, 5503, 5928, 9593, 18671, 40189, 60655, 113586, 172692
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OFFSET
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1,2
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COMMENTS
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For k > 1, numbers such that the digit 5 followed by k-2 occurrences of the digit 0 followed by the digits 57 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 5*10^2 + 57 = 557 is prime.
Initial terms and primes associated:
a(1) = 1, 107;
a(2) = 2, 557;
a(3) = 5, 500057;
a(4) = 8, 500000057;
a(5) = 14, 500000000000057; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[5*10^# + 57] &]
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PROG
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(PARI) isok(k) = isprime(5*10^k + 57); \\ Michel Marcus, Nov 22 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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