A373351 - OEIS

%I #14 Jul 02 2024 01:57:58

%S 1,9,18,21,34,35,36,39,49,62,63,69,70,73,78,80,86,93,99,102,116,122,

%T 123,141,142,143,146,147,150,178,182,185,201,206,223,230,236,238,241,

%U 246,251,267,279,285,292,293,304,309,313,321,326,329,343,346,347,350,355,362,375,380,381,385,389,398

%N Numbers k such that there are no primes among the k-digit numbers consisting of one 1 and all other digits 9.

%C Besides 1, numbers k such that A241018(k) = 0.

%H Robert Israel, <a href="/A373351/b373351.txt">Table of n, a(n) for n = 1..577</a>

%e a(2) = 9 is a term because none of the numbers 199999999, 9199999999, ..., 999999991 are prime.

%p filter:= proc(n) local a,j;

%p a:= 10^n-1;

%p not ormap(j -> isprime(a-8*10^j), [$0..n-1])

%p end proc:

%p select(filter, [$1..400]);

%Y Cf. A241018.

%K nonn,base

%O 1,2

%A _Robert Israel_, Jun 01 2024