Eighty-four is seven times twelve and reduces to twelve and then three. In the Indian and Buddhist traditions it is a number of vast completeness, usually encountered multiplied. Tantric Buddhism venerates the eighty-four Mahasiddhas, the great adepts whose unconventional lives are gathered in Tibetan hagiography. Hatha yoga counts eighty-four classical asanas as the seed-postures chosen, in the traditional account, by Shiva from among eight million four hundred thousand. And the rebirth cosmology of Hinduism and Jainism speaks of eighty-four lakh yonis, eight million four hundred thousand species of embodied life through which the soul may pass, so that human birth is the rare culmination of an immense round.
In chemistry, eighty-four is the atomic number of polonium, discovered in 1898 by Marie and Pierre Curie and named for Poland, Marie's homeland, then partitioned among three empires and not an independent state, the first element ever named for an explicitly political reason.
The whole apparatus of digit-reduction numerology is a twentieth-century invention rather than an inheritance from antiquity. Mrs. L. Dow Balliett published the first systematic version, The Philosophy of Numbers, in 1908, fixing the letter-to-number chart still used today and ruling that eleven and twenty-two must stand as master numbers rather than reduce further; her colleague, the physician Julia Seton, is credited with coining the word numerology itself around 1912.