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If you represent it in Hexadecimal, sure. That's very uncommon in IPv4, but just fine for IPv6.
The default subnet mask would be 255.255.0.0
If this is a default subnet mask, then it would be a class C subnet mask. If you are subnetting a network and this is not the default subnet mask, then it could be either a class A or class B.
The default subnet mask has a standard size. The custom subnet mask allows you to make subnets that are smaller or larger than the default.
The default subnet mask is 255.255.0.0
Default Subnet mask: 255.255.0.0
default subnet mask for 198.25.4.129
It is called a subnet mask. A subnet mask is used for dividing IP addresses into host and network addresses.
2 given subnets
A default subnet mask gives you classful addressing on octet boundaries. A non-default subnet mask implies that you are subnetting a larger network into several smaller ones.
Subnet mask for the above is 255.0.0.0