How to declare std::vector with an 'n' dimensional array?

My thoughts are the following:
for e.g. a two-dimensional array:

int a[9][9];
std::vector<int** a> b;

But what if I have

/* I know, it is usually a bad practise to have more than 2 dimensional arrays, but it can happen, when you need it */
int a[3][4][5][6]; 
std::vector<int**** a> b; // ? this just looks bad