The CAS Registry Mumber 77872-35-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,7,8,7 and 2 respectively; the second part has 2 digits, 3 and 5 respectively. Calculate Digit Verification of CAS Registry Number 77872-35: (7*7)+(6*7)+(5*8)+(4*7)+(3*2)+(2*3)+(1*5)=176 176 % 10 = 6 So 77872-35-6 is a valid CAS Registry Number.