The CAS Registry Mumber 136413-80-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,6,4,1 and 3 respectively; the second part has 2 digits, 8 and 0 respectively. Calculate Digit Verification of CAS Registry Number 136413-80: (8*1)+(7*3)+(6*6)+(5*4)+(4*1)+(3*3)+(2*8)+(1*0)=114 114 % 10 = 4 So 136413-80-4 is a valid CAS Registry Number.