The CAS Registry Mumber 87776-15-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,7,7,7 and 6 respectively; the second part has 2 digits, 1 and 5 respectively. Calculate Digit Verification of CAS Registry Number 87776-15: (7*8)+(6*7)+(5*7)+(4*7)+(3*6)+(2*1)+(1*5)=186 186 % 10 = 6 So 87776-15-6 is a valid CAS Registry Number.