This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A120023 #30 Sep 29 2024 16:06:29 %S A120023 0,1,2,3,4,10,11,17,20,28,41,48,57,58,59,71,208,972,993,1432,2001, %T A120023 2175,2622,3419,3720,4860,7300,7402,14988,15774,18510,22872,52139, %U A120023 77028,149025,172170,239699 %N A120023 Numbers k such that 2*6^k + 1 is prime. %C A120023 If 6^n is of the form T(x,y) = 2xy+x+y [A083487] then 2*6^n+1 is not prime. - _Vincenzo Librandi_, Nov 13 2010 %C A120023 a(1)-a(37) proven prime by the primality proving program LLR. - _Robert Price_, Jan 08 2016 %C A120023 a(38) > 2.5*10^5. - _Robert Price_, Jan 08 2016 %t A120023 Select[Range[0, 2000], PrimeQ[2*6^# + 1] &] (* _Vladimir Joseph Stephan Orlovsky_, Jan 31 2012 *) %o A120023 (PARI) isok(n) = isprime(2*6^n+1); \\ _Michel Marcus_, Jan 08 2016 %Y A120023 Cf. A057472, A120024, A205771. %K A120023 nonn,more %O A120023 1,3 %A A120023 _Pierre CAMI_, Jun 04 2006 %E A120023 More terms from _Pierre CAMI_, Jun 16 2006 %E A120023 a(32)-a(37) from _Robert Price_, Jan 08 2016