What characterizes a fictitious account number?

A fictitious account number is indeed characterized by the fact that it has never existed in reality. This type of account number is typically created for various purposes, such as testing payment systems or for reference in scenarios where a real account is not needed. These numbers help ensure that systems can function properly without the risk of impacting actual customer accounts or sensitive data.

In contrast to the other options, fictitious account numbers are not exclusive to premium services nor are they linked to real customer accounts; their primary characteristic is that they do not correspond to any actual accounts. Additionally, while some fictitious numbers may be generated or used in contexts involving government entities, this is not a defining characteristic of what makes an account number fictitious. Thus, the distinguishing feature is that a fictitious account number has never existed, emphasizing its role as a non-operational or abstract identifier.