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A273924
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Numbers k such that (7*10^k - 13)/3 is prime.
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0
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1, 2, 5, 6, 28, 53, 56, 86, 88, 90, 96, 136, 142, 186, 202, 373, 448, 785, 988, 1263, 1966, 3561, 4768, 9658, 9831, 17797, 42286, 49893, 98007, 129472, 146860
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OFFSET
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1,2
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COMMENTS
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For k>1, numbers n such that the digit 2 followed by k-2 occurrences of the digit 3 followed by the digits 29 is prime (see Example section).
a(32) > 2*10^5.
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LINKS
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EXAMPLE
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5 is in this sequence because (7*10^5 - 13)/3 = 233329 is prime.
Initial terms and primes associated:
a(1) = 1, 19;
a(2) = 2, 229;
a(3) = 5, 233329;
a(4) = 6, 2333329;
a(5) = 28, 23333333333333333333333333329, etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(7*10^# - 13)/3] &]
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PROG
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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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