The CAS Registry Mumber 2531-05-7 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 2,5,3 and 1 respectively; the second part has 2 digits, 0 and 5 respectively. Calculate Digit Verification of CAS Registry Number 2531-05: (6*2)+(5*5)+(4*3)+(3*1)+(2*0)+(1*5)=57 57 % 10 = 7 So 2531-05-7 is a valid CAS Registry Number.