Re: PIN card

Mike Amling wrote:

> Let's say we have an alphabet of d distinct symbols. What's the
> smallest (area) rectangular array of such symbols such that every
> n-symbol sequence of such symbols is present in the array somewhere if
> we allow reading sequences in straight lines in any of the 8 directions
> N, S, E, W, NW, NE, SW, SE?
[snip]
> 2x2 is minimal for d=2, n=2.
> 8x1 is sufficient, and I think minimal, for d=2, n=3.

Cute problem! C'mon, gang; what's the answer?

Sequences generated by linear-feedback shift registers
come close to giving you a d^(n-1)-by-1 table missing
the 000...0 pattern; but that's not much practical help.

-- 
Peter Pearson
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