The CAS Registry Mumber 78687-38-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,8,6,8 and 7 respectively; the second part has 2 digits, 3 and 8 respectively. Calculate Digit Verification of CAS Registry Number 78687-38: (7*7)+(6*8)+(5*6)+(4*8)+(3*7)+(2*3)+(1*8)=194 194 % 10 = 4 So 78687-38-4 is a valid CAS Registry Number.