The CAS Registry Mumber 655251-05-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 6,5,5,2,5 and 1 respectively; the second part has 2 digits, 0 and 5 respectively. Calculate Digit Verification of CAS Registry Number 655251-05: (8*6)+(7*5)+(6*5)+(5*2)+(4*5)+(3*1)+(2*0)+(1*5)=151 151 % 10 = 1 So 655251-05-1 is a valid CAS Registry Number.