Also check out the function exists. It lets you test if a key is in a hash. In this case it would help you debug but it's useful in general for validating hash keys, especially when they come from user input.

I added the following at the end of your script:

if( exists $j{$number} ) {
    say $j{$number};
    say "done";
}
else {
    say "<$number> is not a key in \%j"
}
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Here is the result of running it:

C:\usr\pm\hash>perl 1214633.pl
4
4

<4
> is not a key in %j
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