This block displays some visual variations on the Recamán sequence. Inspiration comes from the Numberphile‘s video The Slightly Spooky Recamán Sequence.

Here is how the Recamán sequence is computed :

```
a(0) = 0;
for n > 0:
a(n) = a(n-1) - n if positive and not already in the sequence,
a(n) = a(n-1) + n otherwise
```

Technically speaking, this block allows me to experiment path animation with CSS.

- D3.js (v.5)
- blockbuilder.org
- Numberphile‘s enlightments