The CAS Registry Mumber 157185-20-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,5,7,1,8 and 5 respectively; the second part has 2 digits, 2 and 0 respectively. Calculate Digit Verification of CAS Registry Number 157185-20: (8*1)+(7*5)+(6*7)+(5*1)+(4*8)+(3*5)+(2*2)+(1*0)=141 141 % 10 = 1 So 157185-20-1 is a valid CAS Registry Number.