The CAS Registry Mumber 77563-20-3 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,7,5,6 and 3 respectively; the second part has 2 digits, 2 and 0 respectively. Calculate Digit Verification of CAS Registry Number 77563-20: (7*7)+(6*7)+(5*5)+(4*6)+(3*3)+(2*2)+(1*0)=153 153 % 10 = 3 So 77563-20-3 is a valid CAS Registry Number.