The CAS Registry Mumber 152561-57-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,5,2,5,6 and 1 respectively; the second part has 2 digits, 5 and 7 respectively. Calculate Digit Verification of CAS Registry Number 152561-57: (8*1)+(7*5)+(6*2)+(5*5)+(4*6)+(3*1)+(2*5)+(1*7)=124 124 % 10 = 4 So 152561-57-4 is a valid CAS Registry Number.