There are three methods of computing Forte number and prime form. Allen Forte published the first in his 1973 book The Structure of Atonal Music, citing a 1961 article by Milton Babbitt.^[1] The second was introduced in Rahn's Basic Atonal Theory and used in Joseph N. Straus's Introduction to Post-Tonal Theory, where it was declared that the two algorithms only differed in five cases: 5-20, 6-Z29, 6-31, 7-20, and 8-26.^[2]

Forte (1973) and Rahn (1980) both list the prime forms of a set as the most left-packed possible version of the set. Forte packs from the left and Rahn packs from the right ("making the small numbers smaller" versus making "the larger numbers smaller").^[3] Programmers tend to prefer Rahn's method, because the Rahn prime is easily computed by comparing sets in binary, whereas Forte's prime requires a more complex algorithm.^[4]