Its called MayamalavaGowla.
It is traditionally the first raagam that is taught to a beginner.The reason is traced back to the prolific composer-Purandaradasa.He is considered as the Sangeetha Pitamaha.
Sangeetha Pitamaha-Purandaradasa
He was the one who formulated the various swara exercises.It is consists of Sarali Varisai,Jhanta Varisai,Thaattu Varisai and so on.All these contain only these seven swaraas.And the various combinations form the Varisais.
The first and foremost being,
S-R-G-M-P-D-N-S
S-N-D-P-M-G-R-S
There's an underlying reason as to why Purandaradasa chose MayamalavaGowla to compose all the basic exercises.It is because,the pitch difference between Ma and Ga was the same as Da-Ni.So that learning could be made easier.