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A205647
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Numbers k such that 3^k + 16 is prime.
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18
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0, 1, 3, 4, 7, 8, 9, 12, 13, 15, 27, 31, 49, 57, 60, 75, 139, 147, 283, 327, 488, 604, 700, 825, 908, 1051, 1064, 1215, 5319, 9669, 10136, 16675, 25656, 28933, 35864, 47671, 68028, 73380, 186223, 194965, 221649, 233059, 240644, 513007, 543128, 551491, 648872, 989124, 994536
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OFFSET
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1,3
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COMMENTS
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LINKS
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FORMULA
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{n: 3^n + 16 is in A000040} = {n: 3^n + 16 is prime} = {n: A000244(n) is prime} = {n: A205646(n) is prime}.
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EXAMPLE
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57 is in the sequence because (3^57) + 16 = 1570042899082081611640534579 is prime.
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MATHEMATICA
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Select[Range[0, 2000], PrimeQ[3^# + 16] &] (* T. D. Noe, Jan 30 2012 *)
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PROG
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CROSSREFS
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Cf. Sequences of numbers k such that 3^k + m is prime:
(m = 32) A219048, (m = -32) A219049, (m = 34) A219050, (m = -34) A219051. Note that if m is a multiple of 3, 3^k + m is also a multiple of 3 (for k greater than 0), and as such isn't prime.
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KEYWORD
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nonn,hard,more
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AUTHOR
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EXTENSIONS
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a(41) discovered by Lelio R Paula, November 2016
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STATUS
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approved
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