The CAS Registry Mumber 153434-54-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,5,3,4,3 and 4 respectively; the second part has 2 digits, 5 and 4 respectively. Calculate Digit Verification of CAS Registry Number 153434-54: (8*1)+(7*5)+(6*3)+(5*4)+(4*3)+(3*4)+(2*5)+(1*4)=119 119 % 10 = 9 So 153434-54-9 is a valid CAS Registry Number.