Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Number | Previous BR No. | Taken into deptal stock | Withdrawn | Disposal |
| --- | --- | --- | --- | --- |
| 17 | 61059.0 | 1963.0 | 1966.0 | Scrapped (1966) |
| 18 | 61181.0 | 1963.0 | 1965.0 | Scrapped (1966) |
| 19 | 61204.0 | 1963.0 | 1966.0 | Scrapped (1966) |
| 20 | 61205.0 | 1963.0 | 1965.0 | Scrapped (1966) |
| 21 | 61233.0 | 1963.0 | 1966.0 | Scrapped (1966) |
| 22 | 61252.0 | 1963.0 | 1964.0 | Scrapped (1966) |
| 23 | 61300.0 | 1963.0 | 1965.0 | Scrapped (1966) |
| 24 (1st) | 61323.0 | 1963.0 | 1963.0 | Scrapped (1964) |
| 24 (2nd) | 61375.0 | 1963.0 | 1966.0 | Scrapped (1966) |
| 25 | 61272.0 | 1965.0 | 1966.0 | Scrapped (1966) |
| 26 | 61138.0 | 1965.0 | 1967.0 | Scrapped (1968) |
| 27 | 61105.0 | 1965.0 | 1966.0 | Scrapped (1966) |
| 28 | 61194.0 | 1965.0 | 1966.0 | Scrapped (1966) |
| 29 | 61264.0 | 1965.0 | 1967.0 | Woodham Brothers , later preserved |
| 30 | 61050.0 | 1966.0 | 1968.0 | Scrapped (1968) |
| 31 (2nd) | 61051.0 | 1966.0 | 1966.0 | Scrapped (1966) |
Question:
Name the total number of previous br number for number 21
Answer:
1.0