# pi

> constant ratio of the circumference of a circle to its diameter

**Wikidata**: [Q167](https://www.wikidata.org/wiki/Q167)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Pi)  
**Source**: https://4ort.xyz/entity/pi-q167


## References

1. [Ludolph van Ceulen und die Ludolphsche Zahl](https://3.141592653589793238462643383279502884197169399375105820974944592.eu/die-geschichte-der-zahl-pi/ludolph-van-ceulen-und-die-ludolphsche-zahl/)
2. Lingua Libre
3. Nuovo soggettario
4. Freebase Data Dumps. 2013
5. [Source](http://datos.bne.es/tema/XX536170.html)
6. [First 100 digits](http://www.math.com/tables/constants/pi.htm)
7. [Decimal expansion of Pi (or, digits of Pi)](https://oeis.org/A000796)
8. BBC Things
9. [Pi Day 2015: meet the man who invented π](https://www.theguardian.com/science/alexs-adventures-in-numberland/2015/mar/14/pi-day-2015-william-jones-the-welshman-who-invented-pi)
10. National Library of Israel
11. [OpenAlex](https://docs.openalex.org/download-snapshot/snapshot-data-format)