The CAS Registry Mumber 161511-61-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,6,1,5,1 and 1 respectively; the second part has 2 digits, 6 and 1 respectively. Calculate Digit Verification of CAS Registry Number 161511-61: (8*1)+(7*6)+(6*1)+(5*5)+(4*1)+(3*1)+(2*6)+(1*1)=101 101 % 10 = 1 So 161511-61-1 is a valid CAS Registry Number.