#! /usr/bin/perl

use strict;
use warnings;

my $n_file = 'path/to/file_with_number.txt';
my $out  = '/path/to/outfile.dat'

my @numbers = ();
my @diameters = ();

# anzahl einlesen;
open(R_N,"<$n_file") or die $!;
my @lines_n = <R_N>;
close R_N;
chomp(@lines_n);
for(my $i = 0; $i < $#lines_n; $i += 2){
  push(@numbers,split(/ /,$lines_n[$i]));
  push(@diameters,split(/ /,$lines_n[$i+1]));
}

open(W_FILE,">$out") or die $!;
for(0..$#numbers){
 print $numbers[$_]," ",$diameters[$_];
}
close W_FILE;