If you're not familiar with the Rowland prime sequence, you can find out about it here. I've created an ugly, procedural monadic verb in J to generate the first n terms in this sequence, as follows:

rowland =: monad define
    result =. 0 $ 0
    t =. 1 $ 7
    while. (# result) < y do.
        a =. {: t
        n =. 1 + # t
        t =. t , a + n +. a
        d =. | -/ _2 {. t
        if. d > 1 do.
            result =. ~. result , d
        end.
    end.
    result
)

This works perfectly, and it indeed generates the first n terms in the sequence. (By n terms, I mean the first n distinct primes.)

Here is the output of rowland 20:

5 3 11 23 47 101 7 13 233 467 941 1889 3779 7559 15131 53 30323 60647 121403 242807

My question is, how can I write this in more idiomatic J? I don't have a clue, although I did write the following function to find the differences between each successive number in a list of numbers, which is one of the required steps. Here it is, although it too could probably be refactored by a more experienced J programmer than I:

diffs =: monad : '}: (|@({.-2&{.) , $:@}.) ^: (1 < #) y'