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 A295032 Numbers k such that 12*10^k - 7 is prime. 0
 0, 1, 2, 4, 5, 8, 11, 21, 25, 105, 191, 305, 463, 704, 1320, 1404, 1580, 1675, 2215, 3475, 6323, 10560, 28817, 30356, 98198 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS For k > 1, numbers such that the digits 11 followed by k-1 occurrences of the digit 9 followed by the digit 3 is prime (see Example section). a(26) > 10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 119w3 EXAMPLE 2 is in this sequence because 12*10^2 - 7 = 1193 is prime. Initial terms and primes associated: a(1) = 0, 5; a(2) = 1, 113; a(3) = 2, 1193; a(4) = 4, 119993; a(5) = 5, 1199993; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[12*10^# - 7 ] &] PROG (PARI) isok(k) = isprime(12*10^k - 7); \\ Michel Marcus, Nov 13 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A182564 A288523 A240179 * A280017 A080136 A080033 Adjacent sequences:  A295029 A295030 A295031 * A295033 A295034 A295035 KEYWORD nonn,more,hard,changed AUTHOR Robert Price, Nov 12 2017 STATUS approved

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Last modified January 18 23:05 EST 2019. Contains 319282 sequences. (Running on oeis4.)