The CAS Registry Mumber 78366-34-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,8,3,6 and 6 respectively; the second part has 2 digits, 3 and 4 respectively. Calculate Digit Verification of CAS Registry Number 78366-34: (7*7)+(6*8)+(5*3)+(4*6)+(3*6)+(2*3)+(1*4)=164 164 % 10 = 4 So 78366-34-4 is a valid CAS Registry Number.