The CAS Registry Mumber 53906-85-7 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 5,3,9,0 and 6 respectively; the second part has 2 digits, 8 and 5 respectively. Calculate Digit Verification of CAS Registry Number 53906-85: (7*5)+(6*3)+(5*9)+(4*0)+(3*6)+(2*8)+(1*5)=137 137 % 10 = 7 So 53906-85-7 is a valid CAS Registry Number.