The CAS Registry Mumber 281655-70-7 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 2,8,1,6,5 and 5 respectively; the second part has 2 digits, 7 and 0 respectively. Calculate Digit Verification of CAS Registry Number 281655-70: (8*2)+(7*8)+(6*1)+(5*6)+(4*5)+(3*5)+(2*7)+(1*0)=157 157 % 10 = 7 So 281655-70-7 is a valid CAS Registry Number.