German Tax Identifier/Code

(?:\b[1-9][0-9]{8}\b)

Matches a 9-digit number of the format NNNNNNNNN, where the first digit can't be zero.

1

(?:\b[1-9][0-9]{2}/?[0-9]{4}/?[0-9]{4}\b)

Matches an 11-digit number of the format NNNNNNNNNNN or NNN/NNNN/NNNN, where the first digit can't be zero.

1