K-39 is the most abundant, constituting about 93 % of the atoms in naturally occurring potassium.
I believe 24 isotopes have been identified with atomic mass ranging from 32 to 55. Only three occur naturally, K39 (93% of the total), K41 (7%) and the radioactive K40 (0.01%). The others have very short half-lives, as small as a few nano-seconds in some cases.
84-k41-89.3