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A373351 Numbers k such that there are no primes among the k-digit numbers consisting of one 1 and all other digits 9.

%I A373351 #14 Jul 02 2024 01:57:58
%S A373351 1,9,18,21,34,35,36,39,49,62,63,69,70,73,78,80,86,93,99,102,116,122,
%T A373351 123,141,142,143,146,147,150,178,182,185,201,206,223,230,236,238,241,
%U A373351 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 A373351 Numbers k such that there are no primes among the k-digit numbers consisting of one 1 and all other digits 9.
%C A373351 Besides 1, numbers k such that A241018(k) = 0.
%H A373351 Robert Israel, <a href="/A373351/b373351.txt">Table of n, a(n) for n = 1..577</a>
%e A373351 a(2) = 9 is a term because none of the numbers 199999999, 9199999999, ..., 999999991 are prime.
%p A373351 filter:= proc(n) local a,j;
%p A373351 a:= 10^n-1;
%p A373351 not ormap(j -> isprime(a-8*10^j), [$0..n-1])
%p A373351 end proc:
%p A373351 select(filter, [$1..400]);
%Y A373351 Cf. A241018.
%K A373351 nonn,base
%O A373351 1,2
%A A373351 _Robert Israel_, Jun 01 2024