Hi. Seems that you need to sort first by alpha-prefix and then numerically. The suggestion below assumes that all items to be sorted have a format that matches m/(\D+)(\d+)/ completely.
See also What is "Schwarzian Transform" (aka Schwartzian) and Schwartzian Transform

use strict;

my @input = qw(d3 d1 d10 d2 d20 d21 a3 d100 d201 a10 a1);


my @sorted =
  map  { $_->[0] . $_->[1] }             # 3) put together elems.
  sort { $a->[0] cmp $b->[0]             # 2) sort alpha prefix
         ||                              #    (if equal, then)
         $a->[1] <=> $b->[1] }           #    sort numeric suffix
  map  { m/(\D+)(\d+)/; [ $1, $2 ] }     # 1) split alpa/numeric-parts
  @input;

print join "\n", @sorted, "\n";

__END__
a1
a3
a10
d1
d2
d3
d10
d20
d21
d100
d201
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@sorted = sort { substr($a, 1) <=> substr($b, 1) } @data
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use Sort::Key::Multi qw(si_keysort);
  # "si" indicates that the sorting keys
  # are a string and an integer

my @sorted = si_keysort { /^(\D*)(\d*)$/ } @data;
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This is really a reply to all who kindly and helpfully answered.
How can this be extended when there is a variable number of alpha characters before any numeric ones?

The solution provided by Perlbotics extends to values where there is at least a non-numeric character followed by at least a numeric character.

You can change it to something else by changing the regular expression (and the anonymous subroutine provided to sort, if required).

Through SMOP