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 A076850 Numbers k such that (10^k + 2)/6 is prime. 0
 1, 2, 3, 4, 6, 10, 12, 15, 33, 55, 56, 61, 154, 201, 462, 570, 841, 848, 1297, 1357, 2008, 2628, 2848, 3111, 6877, 9162 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Some of the larger entries may only correspond to probable primes. a(26) > 8000. - Jon E. Schoenfield, Dec 24 2017 LINKS MATHEMATICA Select[Range[5000], PrimeQ[(10^# + 2) / 6] &] (* Vincenzo Librandi, Sep 24 2016 *) PROG (PARI) isok(n) = isprime((10^n + 2)/6); \\ Michel Marcus, Aug 28 2013 (Magma) [n: n in [0..200] |IsPrime((10^n+2) div 6)]; // Vincenzo Librandi, Sep 24 2016 (Python) from sympy import isprime, prime, nextprime def afind(limit, startk=1):     k, tenk = startk, 10**startk     for k in range(startk, limit+1):         if isprime((tenk + 2)//6):             print(k, end=", ")         tenk *= 10 afind(1000) # Michael S. Branicky, Feb 26 2022 CROSSREFS Sequence in context: A070519 A177913 A098392 * A068482 A068499 A137172 Adjacent sequences:  A076847 A076848 A076849 * A076851 A076852 A076853 KEYWORD nonn,more AUTHOR Ed Pegg Jr, Nov 23 2002 EXTENSIONS More terms from Jason Earls, Nov 24 2002 a(25) from Jon E. Schoenfield, Dec 23 2017 a(26) from Michael S. Branicky, Feb 27 2022 STATUS approved

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Last modified May 19 12:20 EDT 2022. Contains 353833 sequences. (Running on oeis4.)