[seqfan] Re: Anyone have a 3-D "Ulam" spiral?

[Andrew Weimholt]

I suppose you can take the plane of the Ulam Spiral and fold the plane up
into a double spiral with a cross section
as shown below...

          #---#---#---#---#---#---#
                                  |
          #---#---#---#---#---#   #
          |                   |   |
          #   #---#---#---#   #   #
          |   |           |   |   |
          #   #   #---O---#   #   #
          |   |   |           |   |
          #   #   #---#---#---#   #
          |   |                   |
          #   #---#---#---#---#---#
          |
          #---#---#---#---#---#---#

Andrew
~

On Sun, Apr 25, 2021 at 10:03 PM Neil Sloane <njasloane at gmail.com> wrote:

> Dear Sequence Fans,
> In two dimensions there is an obvious way to number the cells of the square
> grid starting at the origin and going around in what is often called the
> square spiral (aka Ulam spiral).  It visits every square once and gradually
> works its way outwards.  Is there a nice analog in 3D?
>
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>