The CAS Registry Mumber 167872-05-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,6,7,8,7 and 2 respectively; the second part has 2 digits, 0 and 5 respectively. Calculate Digit Verification of CAS Registry Number 167872-05: (8*1)+(7*6)+(6*7)+(5*8)+(4*7)+(3*2)+(2*0)+(1*5)=171 171 % 10 = 1 So 167872-05-1 is a valid CAS Registry Number.