The CAS Registry Mumber 78558-84-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,8,5,5 and 8 respectively; the second part has 2 digits, 8 and 4 respectively. Calculate Digit Verification of CAS Registry Number 78558-84: (7*7)+(6*8)+(5*5)+(4*5)+(3*8)+(2*8)+(1*4)=186 186 % 10 = 6 So 78558-84-6 is a valid CAS Registry Number.