The CAS Registry Mumber 183241-72-7 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,8,3,2,4 and 1 respectively; the second part has 2 digits, 7 and 2 respectively. Calculate Digit Verification of CAS Registry Number 183241-72: (8*1)+(7*8)+(6*3)+(5*2)+(4*4)+(3*1)+(2*7)+(1*2)=127 127 % 10 = 7 So 183241-72-7 is a valid CAS Registry Number.