Syntax options:

    MAXVALUE numeric-value | NOMAXVALUE

    The MAXVALUE clause specifies the maximum BIGINT value that the
    sequence can generate. For an ascending sequence, the new maximum
    value must be greater than or equal to the existing RDB$NEXT_
    SEQUENCE_VALUE. For a descending sequence, the new maximum
    value must be greater than or equal to the existing MAXVALUE.
    This ensures that the MAXVALUE is not less than any currently
    issued values. In addition, the numeric value must be between
    -9223372036854775808 and 9223372036854775808. The MAXVALUE must
    be greater than the value specified with the MINVALUE clause.
    The NOMAXVALUE clause specifies that the maximum value for an
    ascending sequence is 9223372036854775808 (minus the cache size),
    and -1 for a descending sequence. The NOMAXVALUE clause is the
    default.