The CAS Registry Mumber 84661-17-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,4,6,6 and 1 respectively; the second part has 2 digits, 1 and 7 respectively. Calculate Digit Verification of CAS Registry Number 84661-17: (7*8)+(6*4)+(5*6)+(4*6)+(3*1)+(2*1)+(1*7)=146 146 % 10 = 6 So 84661-17-6 is a valid CAS Registry Number.