The CAS Registry Mumber 135145-20-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,5,1,4 and 5 respectively; the second part has 2 digits, 2 and 0 respectively. Calculate Digit Verification of CAS Registry Number 135145-20: (8*1)+(7*3)+(6*5)+(5*1)+(4*4)+(3*5)+(2*2)+(1*0)=99 99 % 10 = 9 So 135145-20-9 is a valid CAS Registry Number.