The CAS Registry Mumber 187455-21-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,8,7,4,5 and 5 respectively; the second part has 2 digits, 2 and 1 respectively. Calculate Digit Verification of CAS Registry Number 187455-21: (8*1)+(7*8)+(6*7)+(5*4)+(4*5)+(3*5)+(2*2)+(1*1)=166 166 % 10 = 6 So 187455-21-6 is a valid CAS Registry Number.