The CAS Registry Mumber 171738-37-7 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,7,1,7,3 and 8 respectively; the second part has 2 digits, 3 and 7 respectively. Calculate Digit Verification of CAS Registry Number 171738-37: (8*1)+(7*7)+(6*1)+(5*7)+(4*3)+(3*8)+(2*3)+(1*7)=147 147 % 10 = 7 So 171738-37-7 is a valid CAS Registry Number.