The CAS Registry Mumber 65826-53-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 6,5,8,2 and 6 respectively; the second part has 2 digits, 5 and 3 respectively. Calculate Digit Verification of CAS Registry Number 65826-53: (7*6)+(6*5)+(5*8)+(4*2)+(3*6)+(2*5)+(1*3)=151 151 % 10 = 1 So 65826-53-1 is a valid CAS Registry Number.