The CAS Registry Mumber 2521-76-8 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 2,5,2 and 1 respectively; the second part has 2 digits, 7 and 6 respectively. Calculate Digit Verification of CAS Registry Number 2521-76: (6*2)+(5*5)+(4*2)+(3*1)+(2*7)+(1*6)=68 68 % 10 = 8 So 2521-76-8 is a valid CAS Registry Number.