You mean the "empirical formula"...........
The "empirical formula" is the simplest whole number defining constituent atoms in a species. And it is calculated by taking percentage mass of each element, and dividing thru by atomic mass, and then modifying these percentages to give simple whole numbers.
And thus %Ba = (17.14*g)/(17.14*g+8.86*g)xx100%=65.9%
And thus %Cl = (8.86*g)/(17.14*g+8.86*g)xx100%=34.1%
You will note of course that the percentages sum to 100%. Why "of course?"
And then we assume 100*g of compound and divide thru by the atomic masses of each constituent:
"Moles of barium" = (65.9*g)/(137.3*g*mol^-1)=0.480*mol.
"Moles of chlorine" = (34.10*g)/(35.5*g*mol^-1)=0.960*mol.
If we divide thru by the smallest molar quantity, CLEARLY, we get an empirical formula of BaCl_2...........