The CAS Registry Mumber 237431-65-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 2,3,7,4,3 and 1 respectively; the second part has 2 digits, 6 and 5 respectively. Calculate Digit Verification of CAS Registry Number 237431-65: (8*2)+(7*3)+(6*7)+(5*4)+(4*3)+(3*1)+(2*6)+(1*5)=131 131 % 10 = 1 So 237431-65-1 is a valid CAS Registry Number.