The CAS Registry Mumber 305861-61-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 3,0,5,8,6 and 1 respectively; the second part has 2 digits, 6 and 1 respectively. Calculate Digit Verification of CAS Registry Number 305861-61: (8*3)+(7*0)+(6*5)+(5*8)+(4*6)+(3*1)+(2*6)+(1*1)=134 134 % 10 = 4 So 305861-61-4 is a valid CAS Registry Number.