O número 1 é fator de todos os números, pois qualquer número multiplicado por 1 resulta nele mesmo.
$6 = \underbrace{2}_{fator}x\underbrace{3}_{fator} \ \ = \ \ \style{color:blue}{\underbrace{1}_{fator}}x\underbrace{2}_{fator}x\underbrace{3}_{fator}$
$15 = \underbrace{3}_{fator}x\underbrace{5}_{fator} \ \ = \ \ \style{color:blue}{\underbrace{1}_{fator}}x\underbrace{3}_{fator}x\underbrace{5}_{fator}$
$30 = \underbrace{2}_{fator}x\underbrace{3}_{fator}x\underbrace{5}_{fator} \ \ = \ \ \style{color:blue}{\underbrace{1}_{fator}}x\underbrace{2}_{fator}x\underbrace{3}_{fator}x\underbrace{5}_{fator}$
$60 = \underbrace{2}_{fator}x\underbrace{2}_{fator}x\underbrace{3}_{fator}x\underbrace{5}_{fator} \ \ = \ \ \style{color:blue}{\underbrace{1}_{fator}}x\underbrace{2}_{fator}x\underbrace{2}_{fator}x\underbrace{3}_{fator}x\underbrace{5}_{fator}$