The four parts
SPSN is the fixed opening text. N is the number series. It adds more capacity and does not describe the publication. RRRRRR is the six-digit serial number. The final X position is a check digit used to catch typing mistakes.
How the check digit is calculated
Write the serial as six digits. Starting from the right, multiply each digit by 2, 3, 4, 5, 6 and 7. Add the results. Then subtract the remainder after division by 11 from 11. Use X when the answer is 10, 0 when it is 11, and the number itself for every other answer.
The number series is not part of this calculation. For example, serial 000001 gives 9, 000006 gives X, and 000014 gives 0.
Why the check digit exists
The check digit helps catch common typing and copying mistakes. A correct check digit does not prove that the SPSN was issued or is active. Use the public lookup to check that.
How the number should appear
The official form uses uppercase letters and dashes, for example SPSN-1-000001-9. The lookup may accept small differences in how a number is typed, but the public page always shows the official form.