https://16777217/

  $ man 3 inet_aton

  […]

   inet_aton() converts the Internet host address cp from the IPv4
   numbers-and-dots notation into binary form (in network byte order)
   and stores it in the structure that inp points to.  inet_aton()
   returns nonzero if the address is valid, zero if not.  The address
   supplied in cp can have one of the following forms:

   a.b.c.d   Each of the four numeric parts specifies a byte  of  the
             address;  the bytes are assigned in left-to-right order
             to produce the binary address.

   a.b.c     Parts a and b specify the first two bytes of the  binary
             address.   Part c is interpreted as a 16-bit value that
             defines the rightmost two bytes of the binary address.
             This notation is  suitable  for  specifying  (outmoded)
             Class B network addresses.

   a.b       Part a specifies the first byte of the binary address.
             Part b is interpreted as a 24-bit value that defines the
             rightmost three bytes of the binary address.  This
             notation is suitable for specifying (outmoded) Class A
             network addresses.

   a         The  value  a is interpreted as a 32-bit value that is
             stored directly into the binary address without any byte
             rearrangement.

   In all of the above forms, components of the dotted address can be
   specified in decimal, octal (with a leading 0), or hexadecimal,
   with a leading 0X).  Addresses in any of these forms are
   collectively termed IPV4 numbers-and-dots notation.  The form that
   uses exactly four decimal numbers is referred to as IPv4 dotted-
   decimal notation (or sometimes: IPv4 dotted-quad notation).