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 A271646 Numbers k such that 22*10^k + 7 is prime. 0
 0, 1, 2, 9, 13, 14, 15, 17, 22, 23, 80, 297, 393, 524, 591, 1107, 1135, 1179, 1442, 2819, 3549, 3756, 3837, 4903, 5277, 5639, 7230, 13147, 14828, 16158, 18119, 28880, 99275, 212339, 254639 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS For k>1, numbers such that the digits 22 followed by k-1 occurrences of the digit 0 followed by the digit 7 is prime (see Example section). a(36) > 3*10^5. LINKS Table of n, a(n) for n=1..35. Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 220w7. EXAMPLE 2 is in this sequence because 22*10^2+7 = 227 is prime. Initial terms and primes associated: a(1) = 0, 29; a(2) = 1, 227; a(3) = 2, 2207; a(4) = 9, 22000000007; a(5) = 13, 220000000000007, etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[22*10^# + 7] &] PROG (PARI) is(n)=ispseudoprime(22*10^n + 7) \\ Charles R Greathouse IV, Jun 13 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A233400 A234945 A357729 * A024976 A171234 A287069 Adjacent sequences: A271643 A271644 A271645 * A271647 A271648 A271649 KEYWORD nonn,more AUTHOR Robert Price, Apr 11 2016 EXTENSIONS a(34)-a(35) from Robert Price, Jun 01 2023 STATUS approved

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Last modified December 4 05:09 EST 2023. Contains 367541 sequences. (Running on oeis4.)