The CAS Registry Mumber 155683-77-5 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,5,5,6,8 and 3 respectively; the second part has 2 digits, 7 and 7 respectively. Calculate Digit Verification of CAS Registry Number 155683-77: (8*1)+(7*5)+(6*5)+(5*6)+(4*8)+(3*3)+(2*7)+(1*7)=165 165 % 10 = 5 So 155683-77-5 is a valid CAS Registry Number.