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 A305740 a(n) is the smallest k such that 10^m*k + 1 is prime for all m in 1..n. 0
 1, 1, 4, 7, 7, 170716, 170926, 26373004, 247201983, 10562770680, 118345066231, 54717848613610 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS a(12) > 3*10^11. LINKS EXAMPLE 10^1*1 + 1 = 11 (prime), so a(1) = 1. 10^2*1 + 1 = 101 (also prime), so a(2) = 1 as well. 10^3*1 + 1 = 1001 = 7*143, so a(3) > 1; 10^1*2 + 1 = 21 = 3*7, so a(3) > 2; 10^2*3 + 1 = 301 = 7*43, so a(3) > 3; however, for m = 1..3, 10^m*4 + 1 yields 41, 401, and 4001, each of which is prime, so a(3) = 4. CROSSREFS Cf. A000040 (primes), A124417, A124516. Sequence in context: A201125 A154922 A060409 * A171548 A296565 A198822 Adjacent sequences:  A305737 A305738 A305739 * A305741 A305742 A305743 KEYWORD nonn,hard,more AUTHOR Jon E. Schoenfield, Jun 23 2018 EXTENSIONS a(12) from Giovanni Resta, Jun 25 2018 STATUS approved

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Last modified January 17 09:32 EST 2020. Contains 330949 sequences. (Running on oeis4.)