my $nr = 25;    my $n = 5-1; 
print "dividable by 5  :-)\n" if (1 x $nr) =~ /^(1+)\1{$n}$/;              # works
print "prime\n"               if (1 x $nr) !~ /^(11+)\1+$/;                # works
(1 x $nr) !~ /^(1+)(1*)$ (?{ sq($1)}) (0) /x;                              # works - but not what I want ...
             sub sq  { print  "SQUARE\n"  if ((length($_[0]) * length($_[0])) == $nr) ; }
			 

my $len = 'length($1)-1';			 
print "square2  :-)\n"        if (1 x $nr) =~ /^(1+)\1{$len}$/;            # this won't work 
print "square3  :-)\n"        if (1 x $nr) =~ /^(1+)\1{length($1)-1}$/;    # this won't work .. but what will?!?!?!