The CAS Registry Mumber 161756-30-5 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,6,1,7,5 and 6 respectively; the second part has 2 digits, 3 and 0 respectively. Calculate Digit Verification of CAS Registry Number 161756-30: (8*1)+(7*6)+(6*1)+(5*7)+(4*5)+(3*6)+(2*3)+(1*0)=135 135 % 10 = 5 So 161756-30-5 is a valid CAS Registry Number.