c:\@Work\Perl>perl -wMstrict -le
"my $s = '37 35 55555 37 8 17 16 25 36 37 3840 42 42 42 40';
 print qq{'$s'};
 ;;
 $s =~ s{ (?<= [0-9]{2}) (?= [0-9]{2}) }{ }xmsg;
 print qq{'$s'};
"
'37 35 55555 37 8 17 16 25 36 37 3840 42 42 42 40'
'37 35 55 5 55 37 8 17 16 25 36 37 38 40 42 42 42 40'