factorial

adj, n (mathematics 数) (of the) product of a whole number and all those whole numbers below it 阶乘; 阶乘的; 因数的: factorial 5 (represented as 5!), ie the product of 5 4 3 2 15的阶乘（记作5!, 为54321的乘积）.

facetiously, facetiousness, facia (also fascia), facial, facially, facile, facilitate, facilitation, facility, facing, facsimile, fact, fact-finding, faction, factional, factionalism, factious, factitious, factor, factorable, factorization, factorisation, factorize, factorise, factory, factory farm, factory ship, factotum, factual, factually, faculty, fad, faddiness, faddish, faddy, fade, fade-in, fade-out, faded, faecal (US fecal), faeces (US feces), fag,