The CAS Registry Mumber 104201-77-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,4,2,0 and 1 respectively; the second part has 2 digits, 7 and 7 respectively. Calculate Digit Verification of CAS Registry Number 104201-77: (8*1)+(7*0)+(6*4)+(5*2)+(4*0)+(3*1)+(2*7)+(1*7)=66 66 % 10 = 6 So 104201-77-6 is a valid CAS Registry Number.