David Breyer Singmaster (14 December 1938 – 13 February 2023) was an American-British mathematician who was emeritus professor of mathematics at London South Bank University, England.

[5] In the autumn semester, his number theory teacher Dick Lehmer posed a prize problem which Singmaster won.

[9] The "Polytechnic of the South Bank" had been created from a merger of institutions in 1970, and Singmaster became a lecturer in the Department of Mathematical Sciences.

[11] Around 1972, he attended the Istituto di Matematica in Pisa for a year having won a research scholarship.

[8] The power of conjugation ... was the last point I understood; I remember lying awake thinking about it, seeing that I could move any four edges into the working locations and realising that this completed the general method for restoring the cube to its original state.

[5] Singmaster quickly acquired a Cube (in exchange for a copy of an M. C. Escher book) and was able to solve it by early September 1978.

[16] The booklet contained his mathematical analysis of Rubik's Cube, allowing a solution to be constructed using basic group theory.

[17] In August 1980 he published an expanded 5th edition of the book retitled as Notes on Rubik's "Magic Cube".

[5] Much of the mathematical content of the book was later reworked by Alexander H. Frey in collaboration with Singmaster to create their Handbook of Cubik Math published in 1982.

[5][22] Singmaster had one of the world's largest collections of books on recreational mathematics which he had accumulated starting in the late 1970s.

[25] However the venture lost him "a fair amount of money" and led to prolonged tax negotiations.

[27] He was instrumental in the re-discovery of one of the world's oldest books on puzzles and magic illusions when he came across a reference to the work in a 19th-century manuscript.

The recovered text, De viribus quantitatis (English: On The Powers Of Numbers) was penned by Luca Pacioli, a Franciscan friar who lived around 1500.

In November 1981, Singmaster appeared on the scifi-themed BBC puzzle show The Adventure Game.