Please understand that I am new to the Monastery. That said, why wouldn't something like this work if the data always has spaces between the numbers?

#!/usr/bin/perl

use strict;

while( <DATA> ) {
    my @numbers = split;
    my $half = int(@numbers/2);
    my @first = splice(@numbers,0,$half);
    print "@first\n";
    print "  @numbers\n";
}

__DATA__
105 106 107 108 109 110 111 112 113
1115 1116 1117 1118 1119 1120 1121 1122 1123
12345 12346 12347 12348 12349 12350 12351 12353
[download]

The first snippet just cuts the line in half, but it could easily be adapted to print out lines of X number of values (with continuation rows indented.)

#!/usr/bin/perl

use strict;

my $maxitems = 3;

while( <DATA> ) {
    my @numbers = split;
    my $indent = '';
    while ( @numbers > 0) {
        my @rowdata = splice(@numbers,0,$maxitems);
        print "${indent}@rowdata\n";
        $indent = '  ';
    }
}

__DATA__
105 106 107 108 109 110 111 112 113 116
1115 1116 1117 1118 1119 1120 1121 1122 1123 1125
12345 12346 12347 12348 12349 12350 12351 12353 12355
[download]

UPDATE: I understand that this doesn't answer the question posed (which is interesting in itself) but I have to wonder if that is the right approach to the task at hand to begin with.