The CAS Registry Mumber 131691-37-7 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,1,6,9 and 1 respectively; the second part has 2 digits, 3 and 7 respectively. Calculate Digit Verification of CAS Registry Number 131691-37: (8*1)+(7*3)+(6*1)+(5*6)+(4*9)+(3*1)+(2*3)+(1*7)=117 117 % 10 = 7 So 131691-37-7 is a valid CAS Registry Number.