Here's my attempt at a Sieve of Eratothenes... I don't use grep that much, so I won't claim that this works...

@numbers = (2 .. 1_000_000);
@primes = ( );

while (my $prime = shift @numbers) {
  push @primes,$prime;
  @numbers = grep { ($_ % $prime) != 0 } @numbers;
} 

print $primes;
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