NCR

The number of ways of choosing r objects from n is written nCr, and n and r are the letters usually chosen. By the first half of the 20th century variables were invariably written in italics but Joyce uses small caps for N and R, perhaps reflecting both our tendency as children to notice something is different and our tendency not to notice exactly what it is.

Combination[1] notation in mathematics

Coincidentally, both NCR and tandem (next line) are/were computer companies offering ATM technology.