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A120023
Numbers k such that 2*6^k + 1 is prime.
2
0, 1, 2, 3, 4, 10, 11, 17, 20, 28, 41, 48, 57, 58, 59, 71, 208, 972, 993, 1432, 2001, 2175, 2622, 3419, 3720, 4860, 7300, 7402, 14988, 15774, 18510, 22872, 52139, 77028, 149025, 172170, 239699
OFFSET
1,3
COMMENTS
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
a(1)-a(37) proven prime by the primality proving program LLR. - Robert Price, Jan 08 2016
a(38) > 2.5*10^5. - Robert Price, Jan 08 2016
MATHEMATICA
Select[Range[0, 2000], PrimeQ[2*6^# + 1] &] (* Vladimir Joseph Stephan Orlovsky, Jan 31 2012 *)
PROG
(PARI) isok(n) = isprime(2*6^n+1); \\ Michel Marcus, Jan 08 2016
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Pierre CAMI, Jun 04 2006
EXTENSIONS
More terms from Pierre CAMI, Jun 16 2006
a(32)-a(37) from Robert Price, Jan 08 2016
STATUS
approved