Nope, that's - as far as I can see - just a sequence of increasing integers. Both K and J examples give an array of random integers in 0-1000000 range.

For reference, in J such sequence of integers can be generated with:

        1+i.1000000
    1 2 3 4 5 6 7 8 9 10 ....

or:

        1+i.1000000 1
     1
     2
     3
     4
     5
     6
     7
     8
     9
    10
    ....

To explain the previous examples (and let's use smaller integer for less typing...), the `$` verb is called "shape"/"reshape", and it takes a (list of) values on the right side, and a list of dimensions on the left:

       5 2 $ 10
    10 10
    10 10
    10 10
    10 10
    10 10

if there's not enough values on the right, they are cycled:

       5 2 $ 10 11 12
    10 11
    12 10
    11 12
    10 11
    12 10

which degenerates to repetition if there's only one value on the right. The `~` adjective (called "reflex") modifies a verb to its left in the following way:

       V~ x NB. same as x V x

so `$~10` is the same as `10$10`, which is a list of ten tens. That list is passed to `?`, which is a verb called "roll", which gives a random integer in the 0-(y-1) range when written as `? y`. `y` here can be a scalar, or a list, in which case the roll is performed for each element of the list:

       $~ 10
    10 10 10 10 10 10 10 10 10 10
       ? $~ 10
    1 6 9 4 6 8 8 7 9 4

The dyadic case, ie. `x ? y` is called "deal", which selects `x` elements from `i. y` list at random, without repetitions. `?~ y`, then, effectively shuffles the `i. y` list:

       ?~10
    6 9 7 3 5 1 8 0 4 2

"deal" can be used to shuffle any list, not only the `i. y` sequence, by using the shuffled list as indexes of another list (using `{` verb, called "from"):

       2*i.10
    0 2 4 6 8 10 12 14 16 18
       (?~10){2*i.10
    14 10 18 6 2 12 8 0 16 4

...I know, I know, it is strange. But it's so interestingly mind-bending that I'd be really happy if I had a valid excuse to pour hundreds of hours into learning J properly. Sadly, I don't have anything like that, so I only spread the strangeness from time to time in comments, like I do right now :)

All the primitives (words) are described here: https://code.jsoftware.com/wiki/NuVoc