I wonder if that challenge site is perhaps ProjectEuler. Their problem 28 has a spiral like this. (It starts from the inside, but that's trivial to fix.)

Update: This thread in the J programming mailing list is how I found out about that projecteuler problem.

Update 1008 jan 10: I forgot to tell, here's my reply to that thread

In reply to Re: Spiraling integers by ambrus
in thread Spiraling integers by Elijah

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