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A254441
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Numbers k such that (41*10^k + 49)/9 is prime.
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1
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2, 3, 6, 20, 26, 38, 51, 119, 155, 218, 446, 486, 1211, 1319, 1338, 1365, 1575, 5106, 7019, 9503, 9695, 14304, 15417, 17765, 24222, 25500, 26306, 35238, 93207
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OFFSET
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1,1
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COMMENTS
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For k>1, numbers that begin with the digit 4 followed by k-2 occurrences of the digit 5 followed by the digits 61 are prime (see Example section).
a(30) > 2*10^5.
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LINKS
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EXAMPLE
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3 is in this sequence because (41*10^3 + 49)/9 = 4561 is prime.
Initial terms and primes associated:
a(1) = 2, 461;
a(2) = 3, 4561;
a(3) = 6, 4555561;
a(4) = 20, 455555555555555555561;
a(5) = 26, 455555555555555555555555561, etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(41*10^# + 49)/9] &]
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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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STATUS
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approved
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