The CAS Registry Mumber 7635-10-1 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 7,6,3 and 5 respectively; the second part has 2 digits, 1 and 0 respectively. Calculate Digit Verification of CAS Registry Number 7635-10: (6*7)+(5*6)+(4*3)+(3*5)+(2*1)+(1*0)=101 101 % 10 = 1 So 7635-10-1 is a valid CAS Registry Number.