The CAS Registry Mumber 155939-25-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,5,5,9,3 and 9 respectively; the second part has 2 digits, 2 and 5 respectively. Calculate Digit Verification of CAS Registry Number 155939-25: (8*1)+(7*5)+(6*5)+(5*9)+(4*3)+(3*9)+(2*2)+(1*5)=166 166 % 10 = 6 So 155939-25-6 is a valid CAS Registry Number.