The CAS Registry Mumber 135980-84-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,5,9,8 and 0 respectively; the second part has 2 digits, 8 and 4 respectively. Calculate Digit Verification of CAS Registry Number 135980-84: (8*1)+(7*3)+(6*5)+(5*9)+(4*8)+(3*0)+(2*8)+(1*4)=156 156 % 10 = 6 So 135980-84-6 is a valid CAS Registry Number.