The CAS Registry Mumber 3405-82-1 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 3,4,0 and 5 respectively; the second part has 2 digits, 8 and 2 respectively. Calculate Digit Verification of CAS Registry Number 3405-82: (6*3)+(5*4)+(4*0)+(3*5)+(2*8)+(1*2)=71 71 % 10 = 1 So 3405-82-1 is a valid CAS Registry Number.