Ah - I was confused about your double usage of numbers as array elements and array indices.

To me, it feels as if you have a number $n and want to remove $n elements from @A1 and put them into A2:

use strict;
use Data::Dumper;

my @A1 = qw(a b c d e f g);
my $n = 2;
my @A2 = splice @A1, @A1-$n, $n;

print Dumper [\@A1, \@A2];

__END__
$VAR1 = [
          [
            'a',
            'b',
            'c',
            'd',
            'e'
          ],
          [
            'f',
            'g'
          ]
        ];
[download]

That can be slightly simplified due to the way splice handles a negative OFFSET:

c:\@Work\Perl\monks>perl -wMstrict -le
"use Data::Dumper;
 ;;
 my @A1 = qw(a b c d e f g);
 my $n = 2;
 my @A2 = splice @A1, -$n;
 ;;
 print Dumper [\@A1, \@A2];
"
$VAR1 = [
          [
            'a',
            'b',
            'c',
            'd',
            'e'
          ],
          [
            'f',
            'g'
          ]
        ];
[download]

(If  $n is greater than the number of elements of the array, a run-time error is thrown.)

Update: Actually, the negative offset approach might be significantly better because it throws an error whenever  $n is greater than the number of array elements, whereas the
    splice @A1, @A1-$n, $n
expression produces a silent, possibly unexpected/undesirable aliasing behavior for some values of  $n > @array and doesn't throw an error until  $n is greater than twice the number of elements of the array.

c:\@Work\Perl\monks>perl -wMstrict -le
"use Data::Dump qw(dd);
 ;;
 my @A1 = qw(a b c d e f g);
 my $n = 14;
 my @A2 = splice @A1, @A1-$n, $n;
 ;;
 dd \@A1, \@A2;
"
([], ["a" .. "g"])

c:\@Work\Perl\monks>perl -wMstrict -le
"use Data::Dump qw(dd);
 ;;
 my @A1 = qw(a b c d e f g);
 my $n = 15;
 my @A2 = splice @A1, @A1-$n, $n;
 ;;
 dd \@A1, \@A2;
"
Modification of non-creatable array value attempted, subscript -8 at -
+e line 1.
[download]

---

Give a man a fish:  <%-{-{-{-<

this works, great thank you