The CAS Registry Mumber 197658-51-8 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,9,7,6,5 and 8 respectively; the second part has 2 digits, 5 and 1 respectively. Calculate Digit Verification of CAS Registry Number 197658-51: (8*1)+(7*9)+(6*7)+(5*6)+(4*5)+(3*8)+(2*5)+(1*1)=198 198 % 10 = 8 So 197658-51-8 is a valid CAS Registry Number.