Compound has n-chiral centres with no symmetry in the molecule
Then, No. of Optical Isomers (X)= 2^n
and, No. of Meso-structures (Y)=0
Hence total no. of stereo isomers= X+Y= 2^n
this one is the only one , and there is no such formula to calculate the no. of isomers in organic .
HOPE IT CLEARS
ALL THE BEST ,..