A book of numbers: amid all the species of information technology, how peculiar and powerful an object this is. ???Lo! the raptured arithmetician!??? wrote ??lie de Joncourt in 1762. ???Easily satis???ed, he asks no Brussels lace, nor a coach and six.??? Joncourt???s own contribution was a small quarto volume registering the ???rst 19,999 triangular numbers.