European Community number

Structure

The EC number may be written in a general form as: NNN-NNN-R, where the N represents digits and R is a check digit. The check digit is calculated using the ISBN method. According to this method, the check digit R is the following sum modulo 11:

${\displaystyle R=(N_1+2N_2+3N_3+4N_4+5N_5+6N_6)mod11}$

If the remainder R is equal to 10, that combination of digits is not used for an EC number. To illustrate, the EC number of dexamethasone is 200-003-9. N₁ is 2, N₂ through N₅ are 0, and N₆ is 3.

${\displaystyle \frac{2+2\times 0+3\times 0+4\times 0+5\times 0+6\times 3}{11}=\frac{20}{11}=1+\frac{9}{11}}$

The remainder is 9, which is the check digit.

There is a set of 181 ELINCS numbers (EC numbers starting with 4) for which the checksum by the above algorithm is 10 and the number has not been skipped but issued with a checksum of 1.