The scales of Huseni (Useni) are as follows :
Aarohanam (Ascending) : S R2 G2 M1 P N2 D2 N2 S’
Avarohanam (Descending) : S’ N2 D1 P M1 G2 R2 S
It is a janya raga, derived from Kharaharapriya (see below) which is 22nd on the Melakarta scale.
It is a comparatively rarely sung raga though there exist compositions by major composers. I believe that being very phrase oriented and close to major ragas make elaborations very difficult in this Raga. Tyagaraja has composed a number of kritis like Emani Vegintune, Raghuvira Ranadhira and Rama Ninne Nammi. Swati Thirunal’s Kanakamayam, Arunachala Kavi’s Eppadi Manam Thunindado, Muthuswami Dikshithar’s Shri Kalahistisha are other compositions most often heard in concerts.
I tend to confuse this raga with Bhairavi; it also sounds like Mukhari in some phrases. There is a good analysis of the typical phrases of Huseni and the distinctions between the allied ragas here.
Note : The 12 notes in the octave are named as below. Please note that C is used as Sa for the sake of simplicity as the scale is relative in Carnatic Music. Also note that the scales paint only a superficial picture of the raga as the gamakas(ornamentations) are a very important part of a raga.