The CAS Registry Mumber 83819-56-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,3,8,1 and 9 respectively; the second part has 2 digits, 5 and 6 respectively. Calculate Digit Verification of CAS Registry Number 83819-56: (7*8)+(6*3)+(5*8)+(4*1)+(3*9)+(2*5)+(1*6)=161 161 % 10 = 1 So 83819-56-1 is a valid CAS Registry Number.