The CAS Registry Mumber 7523-57-1 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 7,5,2 and 3 respectively; the second part has 2 digits, 5 and 7 respectively. Calculate Digit Verification of CAS Registry Number 7523-57: (6*7)+(5*5)+(4*2)+(3*3)+(2*5)+(1*7)=101 101 % 10 = 1 So 7523-57-1 is a valid CAS Registry Number.