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A076850 Numbers k such that (10^k + 2)/6 is prime.

%I A076850 #44 Aug 05 2024 06:11:43
%S A076850 1,2,3,4,6,10,12,15,33,55,56,61,154,201,462,570,841,848,1297,1357,
%T A076850 2008,2628,2848,3111,6877,9162,17766,33556
%N A076850 Numbers k such that (10^k + 2)/6 is prime.
%C A076850 Some of the larger entries may only correspond to probable primes.
%C A076850 a(26) > 8000. - _Jon E. Schoenfield_, Dec 24 2017
%t A076850 Select[Range[5000], PrimeQ[(10^# + 2) / 6] &] (* _Vincenzo Librandi_, Sep 24 2016 *)
%o A076850 (PARI) isok(n) = isprime((10^n + 2)/6); \\ _Michel Marcus_, Aug 28 2013
%o A076850 (Magma) [n: n in [0..200] |IsPrime((10^n+2) div 6)]; // _Vincenzo Librandi_, Sep 24 2016
%o A076850 (Python)
%o A076850 from sympy import isprime, prime, nextprime
%o A076850 def afind(limit, startk=1):
%o A076850     k, tenk = startk, 10**startk
%o A076850     for k in range(startk, limit+1):
%o A076850         if isprime((tenk + 2)//6):
%o A076850             print(k, end=", ")
%o A076850         tenk *= 10
%o A076850 afind(1000) # _Michael S. Branicky_, Feb 26 2022
%K A076850 nonn,more
%O A076850 1,2
%A A076850 _Ed Pegg Jr_, Nov 23 2002
%E A076850 More terms from _Jason Earls_, Nov 24 2002
%E A076850 a(25) from _Jon E. Schoenfield_, Dec 23 2017
%E A076850 a(26) from _Michael S. Branicky_, Feb 27 2022
%E A076850 a(27) from _Michael S. Branicky_, Mar 29 2023
%E A076850 a(28) from _Michael S. Branicky_, Aug 05 2024