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A119720
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Numbers n such that 7^n + 2 is semiprime.
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0
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1, 2, 6, 9, 12, 14, 26, 33, 44, 54, 126, 141, 830, 2436, 3534, 3846, 4152, 4460, 4974, 13160, 13200, 13832
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Or, (7^n+2)/3 is prime.
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EXAMPLE
| 12 is OK because 7^12+2=13841287203=3*4613762401 and 4613762401 is prime.
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MATHEMATICA
| Select[Range[2100], PrimeQ[(7^# + 2)/3] &] - Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Jul 22 2006
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CROSSREFS
| Sequence in context: A174682 A153043 A171504 * A173978 A000134 A120701
Adjacent sequences: A119717 A119718 A119719 * A119721 A119722 A119723
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KEYWORD
| nonn,more
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AUTHOR
| Zak Seidov (zakseidov(AT)yahoo.com), Jun 13 2006
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EXTENSIONS
| 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
a(15)-a(22) from Sean A. Irvine (sairvin(AT)xtra.co.nz), Dec 16 2009
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