sub p{my@x;map{my$c=$_;$_%$c||++$x[$_]for@_}@_=2..pop;grep$x[$_]==1,0..$#x}
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sub p{@_=2..pop;my$c;while($_[$c]){@_=($_[$c],grep$_%$_[$c],@_);$c++}@_}
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sub p{@_=2..pop;my$c;@_=($_[$c++],grep$_%$_[$c-1],@_)while$c<@_;@_}
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sub p{grep{my$c=$_;$#_==grep$c%$_,@_}@_=2..pop}