The CAS Registry Mumber 136131-54-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,6,1,3 and 1 respectively; the second part has 2 digits, 5 and 4 respectively. Calculate Digit Verification of CAS Registry Number 136131-54: (8*1)+(7*3)+(6*6)+(5*1)+(4*3)+(3*1)+(2*5)+(1*4)=99 99 % 10 = 9 So 136131-54-9 is a valid CAS Registry Number.