- FIBONACCI
- Eponymous Italian mathematician
- Eponym of a number series that begins 1, 1, 2, 3, 5, 8, ...
- Eponym for a mathematical pattern identified centuries earlier in India
- Like the two 40-Across in the grid for this answer
- Mathematician behind the sequence 1, 1, 2, 3, 5 ...
- Leonardo known for a sequence of numbers