There’s an online game going on, counting the number of collaboration links required to reach mathematician Paul Erdős, actor Kevin Bacon, and heavy metal band Black Sabbath. For example, if you were in a film with Kevin Bacon, your Bacon number is 1. If you were in a film with someone with a Bacon number of 1, your Bacon number is 2, etc. If you coauthored a scientific paper with Paul Erdős, your Erdős number is 1, and the number rises if you have only coauthored with one of Erdős’s collaborators, etc. Sabbath numbers are calculated similarly, based on whether you have recorded or performed music with someone who’s in Black Sabbath.

The combined Erdős-Bacon-Sabbath number is the sum of your Erdős, Bacon, and Sabbath numbers. Mine is 12, according to this calculation:

Erdős number ≤ 3:
I coauthored Marginalia on a theorem of Woodin (2017) with
Ali Enayat, who wrote An improper arithmetically closed Borel subalgebra of P (ω) mod FIN (2011) with
Saharon Shelah, who coauthored Separability properties of almost-disjoint families of sets (1972) with
Paul Erdős.

Bacon number ≤ 4:
I appeared in the closing scene of För min skuld (2011) with
Anna Dalentoft, who played in Upp i det blå (2016) with
Sofia Gällerspång, who appeared in Filth (2013) with
James McAvoy, who was in X-Men: First Class (2011) with
Kevin Bacon.

Sabbath number ≤ 5:
I played double bass on a recording of Sång till friheten (2015) with
Mikael Wiehe, who recorded Clownen (1991) together with
Per Lindvall, who played drums on Since I lost my baby (2014) with
Cliff Richard, who sang on Move it (2006) with
Brian May, who played guitar on When death calls (1989) with
Black Sabbath.