I think I'd do it like this:

   #10#.(#~ 36=*/@|:) 1+(6#3)#:i.3^6
90

In other words, generate all 729 possibilities as lists of digits and
keep those whose product is 36.

That said, technically we don't actually need to combine them into
single numbers:

   #(#~ 36=*/@|:) 1+(6#3)#:i.3^6
90

Thanks,

-- 
Raul

On Mon, Apr 9, 2018 at 1:51 AM, Skip Cave <s...@caveconsulting.com> wrote:
> Here's a fun math challenge on Quora:
>
> Find the number of 6-digit numbers made up of the digits 1, 2, and 3 which
> have no digit recurring three or more times, consecutively?
>
> The link to my answer on Quora is: https://goo.gl/BzBDQe
>
> Skip Cave
> Cave Consulting LLC
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