The CAS Registry Mumber 136135-88-1 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 5 respectively; the second part has 2 digits, 8 and 8 respectively. Calculate Digit Verification of CAS Registry Number 136135-88: (8*1)+(7*3)+(6*6)+(5*1)+(4*3)+(3*5)+(2*8)+(1*8)=121 121 % 10 = 1 So 136135-88-1 is a valid CAS Registry Number.