For any fixed integer k greater-than-or-equal-to 2, we define a statis
tic on partitions called the k-rank. The definition involves the decom
position into successive Durfee squares. Dyson's rank corresponds to t
he 2-rank. Generating function identities are given. The sign of the k
-rank is reversed by an involution which we call k-conjugation. We pro
ve the following partition theorem: the number of self-2k-conjugate pa
rtitions of n is equal to the number of partitions of n with no parts
divisible by 2k and the parts congruent to k (mod 2k) are distinct. Th
is generalizes the well-known result: the number of self-conjugate par
titions of n is equal to the number of partitions into distinct odd pa
rts.