The CAS Registry Mumber 77428-13-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,7,4,2 and 8 respectively; the second part has 2 digits, 1 and 3 respectively. Calculate Digit Verification of CAS Registry Number 77428-13: (7*7)+(6*7)+(5*4)+(4*2)+(3*8)+(2*1)+(1*3)=148 148 % 10 = 8 So 77428-13-8 is a valid CAS Registry Number.