Final answer:
The saying 'if two is company and three is a crowd' is an idiomatic English expression referring to social situations. There is no traditional continuation for four and five; any extensions are humorous and non-standard.
Step-by-step explanation:
The phrase "if two is company and three is a crowd" is a part of English idiomatic expressions and does not literally relate to any mathematical concept. It implies that two people together is an ideal social situation, while three people might be one too many, hence a 'crowd'. There is no standard continuation of this idiom for the numbers four and five, as the original saying highlights the dynamics of social interactions rather than providing a numerical sequence or rule.
However, sometimes people humorously extend the phrase, with various non-standard continuations like "four's a party" and "five's a riot", but these are neither official nor commonly accepted parts of the idiom. The humor lies in creating a progression of more chaotic or involved scenarios as numbers increase. It's important to understand the context and usage of idiomatic expressions when learning a language, as they often don't translate literally.