Yes, it's 4 binary bytes in octal notation. Can read it as 8 * first digit + second digit. the leading \n is a newline character, which is ASCII 10 (octal 12).

use Data::Dump qw(dump);
print dump( pack("c*", 10, 3, 30, 21 ) );   # outputs: "\n\3\36\25"
[download]

Okay, that "\n" isn't octal notation obviously, it's the Perl string escape code.