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 A081715 Numbers n such that 3^n+2 is a semiprime. 2
 6, 7, 11, 12, 20, 27, 28, 40, 44, 60, 71, 84, 108, 118, 145, 156, 160, 211, 263, 295, 296, 304, 306, 316, 351, 474, 488, 495 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(29) >= 514. - Hugo Pfoertner, Jul 24 2019 531, 562, 676, 760, 807, 866, 1059, 1502, 1659, 2539, 2656, 3070, 3163, 4014, 5736, 5966, 6680, 6745, 7192, 7861, 8104, 9703, 10014 are terms of this sequence. - Chai Wah Wu, Oct 18 2019 LINKS EXAMPLE a(1)=6 because 3^6+2=731=17*43, a(2)=7 because 3^7+2=2189=11*199. a(1)=6 because 3^6+2=731=17*43 a(2)=7 because 3^7+2=2189=11*199 a(3)=11 because 3^11+2=177149=7*25307 a(4)=12 because 3^12+2=531443=11*48313 a(5)=20 because 3^20+2=3486784403=58027*60089 a(6)=27 because 3^27+2=7625597484989=11*693236134999 a(7)=28 because 3^28+2=22876792454963=131*174632003473 a(8)=40 because 3^40+2=12157665459056928803=1170408739*10387538177 a(9)=44 because 3^44+2=984770902183611232883=21577*45639843452917979 a(10)=60 because 3^60+2=42391158275216203514294433203=89*476305149159732623756117227 a(11)=71 because 3^71+2=7509466514979724803946715958257549=7*1072780930711389257706673708322507 a(12)=84 because 3^84+2=11972515182562019788602740026717047105683=13483993*887905769645684315365837109728331 a(13)=108 because 3^108+2=3381391913522726342930221472392241170198527451848563=671633*5034582746116891729456744192724659405059798211 a(14)=118 because 3^118+2=199667811101603467823686647723289448859052847504205678491=17*11745165358917851048452155748428791109356049853188569323 a(15)=145 because 3^145+2=1522586358169246802159262479225089070726226750574991661790882326344645=5*304517271633849360431852495845017814145245350114998332358176465268929 a(16)=156 because 3^156+2=269721605590607563262106870407286853611938890184108047911269431464974473523=21883136019044570108827*12325546272521124629737118652366725946328428459583049 a(17)=160 because 3^160+2=21847450052839212624230656502990235142567050104912751880812823948662932355203=19*1149865792254695401275297710683696586450897373942776414779622313087522755537 a(18)=211 because 3^211+2=47052721287394587764057094854672253553918218437190874778408030747195017485692977810906266281547645149=97*485079600900975131588217472728579933545548643682380152354721966465928015316422451658827487438635517 a(19)=263 because 3^263+2=304011485348815530556923313708989269910796626718253224787639751028488890841299195402970869140037716024202112537180443065484429=7*43430212192687932936703330529855609987256660959750460683948535861212698691614170771852981305719673717743158933882920437926347 a(20)=295 because 3^295+2=563339419994190847700930153835754386693266237141306322927902016783411511018514718493004963603658195013376479179415613344911575031957595780109=3535513*159337391771488564092659298335419608609349261943402929908022404891004929417177851840172830252259911083165718575894251653129708484159893 PROG (PARI) for(n=1, 295, if(bigomega(3^n+2)==2, print1(n", "))) - Herman Jamke (hermanjamke(AT)fastmail.fm), Apr 25 2007 CROSSREFS Cf. A001358, A051783, A057735, A080443, A080892. Sequence in context: A243489 A164018 A156793 * A054504 A190612 A270431 Adjacent sequences:  A081712 A081713 A081714 * A081716 A081717 A081718 KEYWORD more,hard,nonn AUTHOR Hugo Pfoertner, Apr 04 2003 EXTENSIONS 2 more terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Apr 25 2007 More terms from Sean A. Irvine, Mar 21 2010 STATUS approved

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Last modified December 9 03:23 EST 2021. Contains 349625 sequences. (Running on oeis4.)