The CAS Registry Mumber 405-25-4 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 4,0 and 5 respectively; the second part has 2 digits, 2 and 5 respectively. Calculate Digit Verification of CAS Registry Number 405-25: (5*4)+(4*0)+(3*5)+(2*2)+(1*5)=44 44 % 10 = 4 So 405-25-4 is a valid CAS Registry Number.