The CAS Registry Mumber 1020253-71-7 includes 10 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 7 digits, 1,0,2,0,2,5 and 3 respectively; the second part has 2 digits, 7 and 1 respectively. Calculate Digit Verification of CAS Registry Number 1020253-71: (9*1)+(8*0)+(7*2)+(6*0)+(5*2)+(4*5)+(3*3)+(2*7)+(1*1)=77 77 % 10 = 7 So 1020253-71-7 is a valid CAS Registry Number.