I think that undef is not prime. :)

But at 47 characters I think MeowChow still won't be beat: 

sub sieve {
  sub p{$_[0],@_>1?p(grep$_%$_[0],@_):()}p 2..pop
}

[download]

In reply to Re: Re: (Golf): Sieve of Eratosthenes by chipmunk
in thread (Golf): Sieve of Eratosthenes by tilly

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