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 A272622 Numbers k such that 9*10^k + 19 is prime. 0
 1, 2, 4, 5, 10, 14, 25, 34, 40, 63, 74, 129, 149, 345, 370, 425, 477, 627, 951, 1610, 2564, 2689, 4227, 7300, 7444, 8360, 16541, 21187, 25685, 31803, 89858, 92821 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For k>1, numbers n such that the digit 9 followed by k-2 occurrences of the digit 0 followed by the digits 19 is prime (see Example section). a(33) > 2*10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 90w19. EXAMPLE 4 is in this sequence because 9*10^4+19 = 90019 is prime. Initial terms and primes associated: a(1) = 1, 109; a(2) = 2, 919; a(3) = 4, 90019; a(4) = 5, 900019; a(5) = 10, 90000000019, etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[9*10^# + 19] &] PROG (PARI) is(n)=ispseudoprime(9*10^n + 19) \\ Charles R Greathouse IV, Jun 13 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A329136 A067935 A228893 * A097133 A023165 A058299 Adjacent sequences:  A272619 A272620 A272621 * A272623 A272624 A272625 KEYWORD nonn,more AUTHOR Robert Price, May 03 2016 STATUS approved

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Last modified November 30 18:59 EST 2021. Contains 349424 sequences. (Running on oeis4.)