The CAS Registry Mumber 137987-34-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,7,9,8 and 7 respectively; the second part has 2 digits, 3 and 4 respectively. Calculate Digit Verification of CAS Registry Number 137987-34: (8*1)+(7*3)+(6*7)+(5*9)+(4*8)+(3*7)+(2*3)+(1*4)=179 179 % 10 = 9 So 137987-34-9 is a valid CAS Registry Number.