How do I access a specific element of a supersorted array?
If you run mySortedArray through the | values filter, it will reset the keys:
{% set mySortedArray = myArray | supersort | values %}

mySortedArray = array(6) {
    [0]=int(1)
    [1]=int(2)
    [2]=int(3)
    [3]=int(5)
    [4]=int(7)
    [5]=int(9)
}