One of the charms of living in an old town or city is finding new routes to familiar places. It’s also one of the charms of maths. Suppose a three-armed star sprouts three half-sized arms from the end of each of its three arms. And then sprouts three quarter-sized arms from the end of each of its nine new arms. And so on. This is what happens:

Three-armed star

3-Star sprouts more arms

Sprouting 3-Star #3

Sprouting 3-Star #4

Sprouting 3-Star #5

Sprouting 3-Star #6

Sprouting 3-Star #7

Sprouting 3-Star #8

Sprouting 3-Star #9

Sprouting 3-Star #10

Sprouting 3-Star #11 — the Sierpiński triangle

Sprouting 3-star (animated)

The final stage is a famous fractal called the Sierpiński triangle — the sprouting 3-star is a new route to a familiar place. But what happens when you trying sprouting a four-armed star in the same way? This does:

Four-armed star #1

Sprouting 4-Star #2

Sprouting 4-Star #3

Sprouting 4-Star #4

Sprouting 4-Star #5

Sprouting 4-Star #6

Sprouting 4-Star #7

Sprouting 4-Star #8

Sprouting 4-Star #9

Sprouting 4-Star #10

Sprouting 4-star (animated)

There’s no obvious fractal with a sprouting 4-star. Not unless you dis-arm the 4-star in some way. For example, you can ban any new arm sprouting in the same direction as the previous arm:

Dis-armed 4-star (+0) #1

Dis-armed 4-Star (+0) #2

Dis-armed 4-Star (+0) #3

Dis-armed 4-Star (+0) #4

Dis-armed 4-Star (+0) #5

Dis-armed 4-Star (+0) #6

Dis-armed 4-Star (+0) #7

Dis-armed 4-Star (+0) #8

Dis-armed 4-Star (+0) #9

Dis-armed 4-Star (+0) #10

Dis-armed 4-star (+0) (animated)

Once again, it’s a new route to a familiar place (for keyly committed core components of the Overlord-of-the-Über-Feral community, anyway). Now try banning an arm sprouting one place clockwise of the previous arm:

Dis-armed 4-Star (+1) #1

Dis-armed 4-Star (+1) #2

Dis-armed 4-Star (+1) #3

Dis-armed 4-Star (+1) #4

Dis-armed 4-Star (+1) #5

Dis-armed 4-Star (+1) #6

Dis-armed 4-Star (+1) #7

Dis-armed 4-Star (+1) #8

Dis-armed 4-Star (+1) #9

Dis-armed 4-Star (+1) #10

Dis-armed 4-Star (+1) (animated)

Again it’s a new route to a familiar place. Now trying banning an arm sprouting two places clockwise (or anti-clockwise) of the previous arm:

Dis-armed 4-Star (+2) #1

Dis-armed 4-Star (+2) #2

Dis-armed 4-Star (+2) #3

Dis-armed 4-Star (+2) #4

Dis-armed 4-Star (+2) #5

Dis-armed 4-Star (+2) #6

Dis-armed 4-Star (+2) #7

Dis-armed 4-Star (+2) #8

Dis-armed 4-Star (+2) #9

Dis-armed 4-Star (+2) #10

Dis-armed 4-Star (+2) (animated)

Once again it’s a new route to a familiar place. And what happens if you ban an arm sprouting three places clockwise (or one place anti-clockwise) of the previous arm? You get a mirror image of the Dis-armed 4-Star (+1):

Dis-armed 4-Star (+3)

Here’s the Dis-armed 4-Star (+1) for comparison:

Dis-armed 4-Star (+1)

**Elsewhere other-accessible**

• Boole(b)an #2 — other routes to the fractals seen above