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Search: id:A119720
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| A119720 |
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Numbers n such that 7^n + 2 is semiprime. |
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+0
1
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| 1, 2, 6, 9, 12, 14, 26, 33, 44, 54, 126, 141, 830, 2436
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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Or, (7^n+2)/3 is prime.
Next term is bigger than 2100.
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EXAMPLE
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12 is OK because 7^12+2=13841287203=3*4613762401 and 4613762401 is prime.
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MATHEMATICA
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Select[Range[2100], PrimeQ[(7^# + 2)/3] &] - Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Jul 22 2006
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CROSSREFS
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Adjacent sequences: A119717 A119718 A119719 this_sequence A119721 A119722 A119723
Sequence in context: A026348 A032713 A086939 this_sequence A000134 A120701 A112870
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KEYWORD
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more,nonn,less
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AUTHOR
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Zak Seidov (zakseidov(AT)yahoo.com), Jun 13 2006
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EXTENSIONS
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More terms from Stefan Steinerberger (stefan.steinerberger(AT)gmail.com) and Joshua Zucker (joshua.zucker(AT)stanfordalumni.org), Jun 21 2006
a(14) from Herman Jamke (hermanjamke(AT)fastmail.fm), Mar 30 2008
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