The CAS Registry Mumber 136774-20-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,6,7,7 and 4 respectively; the second part has 2 digits, 2 and 0 respectively. Calculate Digit Verification of CAS Registry Number 136774-20: (8*1)+(7*3)+(6*6)+(5*7)+(4*7)+(3*4)+(2*2)+(1*0)=144 144 % 10 = 4 So 136774-20-4 is a valid CAS Registry Number.