While I don't condone regexes on HTML, the general idea is:

($nth_chunk) = $text =~ /(?:PREFACE(MATCH)POSTFIX){N}/;
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In your case, that'd be:

my ($number13) = $text =~ /(?:<TD nowrap>(.*?)</TD>\n){13}/;
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The reason it works is because a capturing group INSIDE a quantifier keeps on overwriting the associated $DIGIT variable on each repetition. Here's a simpler example:

"abcdef" =~ /(.)/;   # $1 is "a"
"abcdef" =~ /(.)+/;  # $1 is "f"
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