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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

Table of n, a(n) for n=1..12.

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.)