The CAS Registry Mumber 1696-34-0 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,6,9 and 6 respectively; the second part has 2 digits, 3 and 4 respectively. Calculate Digit Verification of CAS Registry Number 1696-34: (6*1)+(5*6)+(4*9)+(3*6)+(2*3)+(1*4)=100 100 % 10 = 0 So 1696-34-0 is a valid CAS Registry Number.