The CAS Registry Mumber 25765-21-3 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,5,7,6 and 5 respectively; the second part has 2 digits, 2 and 1 respectively. Calculate Digit Verification of CAS Registry Number 25765-21: (7*2)+(6*5)+(5*7)+(4*6)+(3*5)+(2*2)+(1*1)=123 123 % 10 = 3 So 25765-21-3 is a valid CAS Registry Number.