The CAS Registry Mumber 78623-42-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,8,6,2 and 3 respectively; the second part has 2 digits, 4 and 2 respectively. Calculate Digit Verification of CAS Registry Number 78623-42: (7*7)+(6*8)+(5*6)+(4*2)+(3*3)+(2*4)+(1*2)=154 154 % 10 = 4 So 78623-42-4 is a valid CAS Registry Number.