IP address can be written 121 ways

The list lists four different ways: dotted, decimal, hex and octal. The other 117 entries are just combinations of the four.

Also I didn't know you could group sub-groups, e.g. http://209.0xd8.59120, http://209.0xd8e6f0 and http://0xd1d8e6f0

I personally found it surprising that the formats can be mixed arbitrarily within dotted notation.

The site is dead (for me) but I guess it is "just" about IPv4 and there is something I learned about IPv4 notation that has been hidden for me for the last 30 years:

1.1 expands to 1.0.0.1

1.1.1 expands to 1.1.0.1

obviously FF not running these through POSIX inet_pton

"The inet_pton() function does not accept other formats (such as the octal numbers, hexadecimal numbers, and fewer than four numbers that inet_addr() accepts)."