The CAS Registry Mumber 70665-83-7 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 5 respectively; the second part has 2 digits, 8 and 3 respectively. Calculate Digit Verification of CAS Registry Number 70665-83: (7*7)+(6*0)+(5*6)+(4*6)+(3*5)+(2*8)+(1*3)=137 137 % 10 = 7 So 70665-83-7 is a valid CAS Registry Number.