For purposes of paragraph (1), the term “small employer” means, with respect to a calendar year and a plan year, an employer who employed an average of at least 2 but not more than 50 employees on business days during the preceding calendar year and who employs at least 2 employees on the first day of the plan year. For purposes of the preceding sentence, all persons treated as a single employer under subsection (b), (c), (m), or (o) of section
414 shall be treated as one employer.