The CAS Registry Mumber 53654-26-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 5,3,6,5 and 4 respectively; the second part has 2 digits, 2 and 6 respectively. Calculate Digit Verification of CAS Registry Number 53654-26: (7*5)+(6*3)+(5*6)+(4*5)+(3*4)+(2*2)+(1*6)=125 125 % 10 = 5 So 53654-26-5 is a valid CAS Registry Number.