The CAS Registry Mumber 53666-02-7 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 5,3,6,6 and 6 respectively; the second part has 2 digits, 0 and 2 respectively. Calculate Digit Verification of CAS Registry Number 53666-02: (7*5)+(6*3)+(5*6)+(4*6)+(3*6)+(2*0)+(1*2)=127 127 % 10 = 7 So 53666-02-7 is a valid CAS Registry Number.