Even with this added difficulty, the crows continued to produce recursive sequences more often than random ones, further supporting the idea that their ability went beyond basic memorization.

Some strange mathematical sequences are always whole numbers — until they’re not. The puzzling patterns have revealed ties to graph theory and prime numbers, awing mathematicians.

A multi-institutional research team found the cognitive ability to represent recursive sequences occurs in humans and non-human primates across age, education, culture and species.