The CAS Registry Mumber 64156-20-3 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 6,4,1,5 and 6 respectively; the second part has 2 digits, 2 and 0 respectively. Calculate Digit Verification of CAS Registry Number 64156-20: (7*6)+(6*4)+(5*1)+(4*5)+(3*6)+(2*2)+(1*0)=113 113 % 10 = 3 So 64156-20-3 is a valid CAS Registry Number.