The CAS Registry Mumber 3240-17-3 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 3,2,4 and 0 respectively; the second part has 2 digits, 1 and 7 respectively. Calculate Digit Verification of CAS Registry Number 3240-17: (6*3)+(5*2)+(4*4)+(3*0)+(2*1)+(1*7)=53 53 % 10 = 3 So 3240-17-3 is a valid CAS Registry Number.