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A270929
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Numbers k such that (16*10^k - 31)/3 is prime.
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496
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1, 2, 3, 4, 15, 20, 24, 32, 38, 40, 63, 93, 104, 194, 208, 514, 535, 600, 928, 1300, 1485, 1780, 2058, 3060, 3356, 3721, 6662, 11552, 15482, 23000, 27375, 34748, 57219, 61251, 85221, 99656, 103214, 103244, 276537
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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 3 followed by the digits 23 is prime (see Example section).
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LINKS
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EXAMPLE
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3 is in this sequence because (16*10^3 - 31)/3 = 5323 is prime.
Initial terms and primes associated:
a(1) = 1, 43;
a(2) = 2, 523;
a(3) = 3, 5323;
a(4) = 4, 53323;
a(5) = 15, 5333333333333323;
a(6) = 20, 533333333333333333323, etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(16*10^# - 31)/3] &]
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PROG
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(PARI) isok(n) = ispseudoprime((16*10^n - 31)/3); \\ Michel Marcus, Mar 26 2016
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CROSSREFS
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KEYWORD
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nonn,base,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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