It isn't the easiest to understand, but that's very nice outside the box thinking!

Update: minor niggles: use $#a since that's what you mean — and please, please, use better variable names.

my @list = ( 41888, 41889, 41890, 41892, 41895 );
my @missing = map { ( $list[ $_ - 1 ] + 1 ) .. ( $list[ $_ ] - 1 ) } 1
+ .. $#list;
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