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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.
1
1, 9, 18, 21, 34, 35, 36, 39, 49, 62, 63, 69, 70, 73, 78, 80, 86, 93, 99, 102, 116, 122, 123, 141, 142, 143, 146, 147, 150, 178, 182, 185, 201, 206, 223, 230, 236, 238, 241, 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
OFFSET
1,2
COMMENTS
Besides 1, numbers k such that A241018(k) = 0.
LINKS
EXAMPLE
a(2) = 9 is a term because none of the numbers 199999999, 9199999999, ..., 999999991 are prime.
MAPLE
filter:= proc(n) local a, j;
a:= 10^n-1;
not ormap(j -> isprime(a-8*10^j), [$0..n-1])
end proc:
select(filter, [$1..400]);
CROSSREFS
Cf. A241018.
Sequence in context: A316438 A208135 A306382 * A222623 A141469 A046412
KEYWORD
nonn,base
AUTHOR
Robert Israel, Jun 01 2024
STATUS
approved