The CAS Registry Mumber 70664-42-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,0,6,6 and 4 respectively; the second part has 2 digits, 4 and 2 respectively. Calculate Digit Verification of CAS Registry Number 70664-42: (7*7)+(6*0)+(5*6)+(4*6)+(3*4)+(2*4)+(1*2)=125 125 % 10 = 5 So 70664-42-5 is a valid CAS Registry Number.