where
is the unitary divisor function. Hagis
(1971) and García (1987) give 82 such pairs. The first few are (114, 126),
(1140, 1260), (18018, 22302), (32130, 40446), ... (OEIS A002952
and A002953; Pedersen).
On Jan. 30, 2004, Y. Kohmoto discovered the largest known unitary amicable pair, where each member has 317 digits.
Kohmoto calls a unitary amicable pair whose members are squareful a proper unitary amicable pair.