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 A270613 Numbers k such that (68*10^k + 7)/3 is prime. 500
 1, 2, 3, 4, 7, 10, 24, 25, 29, 34, 35, 37, 46, 49, 88, 103, 290, 381, 484, 696, 751, 886, 999, 1750, 5062, 6214, 9740, 12558, 16551, 24674, 28600, 37427, 48032, 61991, 70148, 72516, 99441, 179656 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers such that the digits 22 followed by k-1 occurrences of the digit 6 followed by the digit 9 is prime (see Example section). a(39) > 2*10^5. LINKS Makoto Kamada, Search for 226w9. EXAMPLE 3 is in this sequence because (68*10^3+7)/3 = 22669 is prime. Initial terms and primes associated: a(1) = 1, 229; a(2) = 2, 2269; a(3) = 3, 22669; a(4) = 4, 226669; a(5) = 7, 226666669, etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(68*10^# + 7)/3] &] PROG (PARI) lista(nn) = for(n=1, nn, if(ispseudoprime((68*10^n + 7)/3), print1(n, ", "))); \\ Altug Alkan, Mar 20 2016 CROSSREFS Cf. A056654, A268448, A269303, A270339. Sequence in context: A094863 A094862 A104722 * A296446 A226387 A102282 Adjacent sequences:  A270610 A270611 A270612 * A270614 A270615 A270616 KEYWORD nonn,more AUTHOR Robert Price, Mar 20 2016 EXTENSIONS a(38) from Robert Price, Jan 16 2020 STATUS approved

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Last modified March 28 07:59 EDT 2020. Contains 333079 sequences. (Running on oeis4.)