The CAS Registry Mumber 148437-91-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,4,8,4,3 and 7 respectively; the second part has 2 digits, 9 and 1 respectively. Calculate Digit Verification of CAS Registry Number 148437-91: (8*1)+(7*4)+(6*8)+(5*4)+(4*3)+(3*7)+(2*9)+(1*1)=156 156 % 10 = 6 So 148437-91-6 is a valid CAS Registry Number.