Decompose the number A and the number B into prime factors: number A=2*2*3*5*a, number B=2*3*7*a. What is the least common multiple of two numbers A and B?
把甲数和乙数分别分解质因数：甲数=2*2*3*5*a，乙数=2*3*7*a．甲乙两数的最小公倍数是多少a
<result>420</result>