The CAS Registry Mumber 1017778-81-2 includes 10 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 7 digits, 1,0,1,7,7,7 and 8 respectively; the second part has 2 digits, 8 and 1 respectively. Calculate Digit Verification of CAS Registry Number 1017778-81: (9*1)+(8*0)+(7*1)+(6*7)+(5*7)+(4*7)+(3*8)+(2*8)+(1*1)=162 162 % 10 = 2 So 1017778-81-2 is a valid CAS Registry Number.