You can use 'g' modifier to the regexp, and then it could returns an array

my $a = '059057034037063107105003046039039036107063035046';
my @nums = split /(\d{3})/g,$a;
[download]

Hope this helps
Hopes
Update Yes, I didn't notice it.
My first script returns empty values too because of the split.

If you want to use split, you can try:

my @nums = grep $_,split /(\d{3})/g,$a;
[download]

but is better without split

my @nums = $a=~/\d{3}/g;
[download]

Regards