The CAS Registry Mumber 18735-25-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,8,7,3 and 5 respectively; the second part has 2 digits, 2 and 5 respectively. Calculate Digit Verification of CAS Registry Number 18735-25: (7*1)+(6*8)+(5*7)+(4*3)+(3*5)+(2*2)+(1*5)=126 126 % 10 = 6 So 18735-25-6 is a valid CAS Registry Number.