Bright and early on the first Saturday in January, Tomas Rokicki and a few hundred fellow enthusiasts gathered in a vast lecture hall at the Moscone Centre in downtown San Francisco. A big math conference was underway and Rokicki, a retired programmer, had helped organise a two-day special session about “serious recreational mathematics” celebrating the 50th anniversary of the Rubik’s Cube. Erno Rubik, the Cube’s inventor, appeared via videoconference from the south of Spain.

Rokicki asked Rubik, a Hungarian architect, designer, sculptor and retired professor, about the first time he solved the cube: “Did you solve corners-first?”