Adjective
lacunary (comparative more lacunary, superlative most lacunary)
(chiefly mathematics) Of, pertaining to, or having characteristics of a lacuna.
It takes on every complex number excepting 0 as value; that is, 0 is a lacunary value of the exponential function. Source: Internet
When an exception exists, it is called a lacunary value of the function. Source: Internet