why the object is vector?

Question

> x=c(1,2,3,4,5)  
> x1=list(n1=1,n2=2,n3=x)  
> is.vector(x1)  

[1] TRUE

> is.list(x1)  

[1] TRUE

Answer 1

> is.atomic(x1)
[1] FALSE

From the R language definition, lists are generic vectors, but not atomic vectors.