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Search: id:A080892
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| A080892 |
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Numbers n such that 3^n-2 is a semiprime. |
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+0
2
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| 3, 8, 10, 12, 13, 15, 16, 19, 20, 21, 25, 28, 39, 42, 44, 48, 55, 57, 60, 66, 67, 76, 78, 85, 118, 130, 156, 162, 212, 214, 218, 228, 244, 330, 352, 357, 376, 386, 388, 464, 480, 525, 545, 552, 644, 742, 793, 813, 815, 893
(list; graph; listen)
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OFFSET
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1,1
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LINKS
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Herman Jamke and others, Illustration of first 42 terms
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EXAMPLE
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a(1)=3 because 3^3-2=25=5*5
a(2)=8 because 3^8-2=6559=7*937
a(3)=10 because 3^10-2=59047=137*431
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MATHEMATICA
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Do[f = 3^n - 2; If[ !PrimeQ[f], s = FactorIntegerECM[f]; If[PrimeQ[s] && PrimeQ[f/s], Print[n]]], {n, 2, 10^3}] - Ryan Propper (rpropper(AT)stanford.edu), May 11 2007
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PROGRAM
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(PARI) for(n=1, 200, if(bigomega(3^n-2)==2, print1(n", "))) - Herman Jamke (hermanjamke(AT)fastmail.fm), Apr 02 2007
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CROSSREFS
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Cf. A001358, A014224, A014232, A080798.
Sequence in context: A067569 A127518 A007284 this_sequence A074186 A064147 A122529
Adjacent sequences: A080889 A080890 A080891 this_sequence A080893 A080894 A080895
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KEYWORD
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more,nonn
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AUTHOR
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Hugo Pfoertner (hugo(AT)pfoertner.org), Mar 30 2003
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EXTENSIONS
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Corrected and extended by Herman Jamke (hermanjamke(AT)fastmail.fm) and Ryan Propper (rpropper(AT)stanford.edu), Apr 01 2007
Further terms from Ryan Propper (rpropper(AT)stanford.edu), Apr 01 2007<br>
Corrected and extended by Herman Jamke (hermanjamke(AT)fastmail.fm), Apr 19 2007
More terms from Ryan Propper (rpropper(AT)stanford.edu), May 11 2007
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