- Eta Aquilae (Wikipedia)
Eta Aquilae (η Aql, η Aquilae) is a multiple star in the equatorial constellation of Aquila, the eagle. It was once part of the former constellation Antinous. Its apparent visual magnitude varies between 3.49 and 4.3, making it one of the brighter members of Aquila. Based upon parallax measurements made by the Gaia spacecraft on its third data release (DR3), this star is located at a distance of roughly 272 parsecs (890 light-years). The primary component is a Classical Cepheid variable.
- Catalan number (Wikipedia)
In combinatorial mathematics, the Catalan numbers are a sequence of natural numbers that occur in various counting problems, often involving recursively defined objects. They are named after the French-Belgian mathematician Eugène Charles Catalan.