We investigate a (potentially infinite) series of subfactors, called 3 n subfactors, including A 4 , A 7 , and the Haagerup subfactor as the first three members corresponding to n = 1, 2, 3. Generalizing our previous work for odd n, we further develop a Cuntz algebra method to construct 3 n subfactors and show that the classification of the 3 n subfactors and related fusion categories is reduced to explicit polynomial equations under a mild assumption, which automatically holds for odd n. In particular, our method with n = 4 gives a uniform construction of 4 finite depth subfactors, up to dual, without intermediate subfactors of index 3 + √ 5. It also provides a key step for a new construction of the Asaeda-Haagerup subfactor due to Grossman, Snyder, and the author.