Table:
text: LNER Thompson Class B1
Departmental service
Departmental service
Number_ Previous_BR_No_ Taken_into_deptal_stock Withdrawn Disposal
17 61059 1963 1966 Scrapped (1966)
18 61181 1963 1965 Scrapped (1966)
19 61204 1963 1966 Scrapped (1966)
20 61205 1963 1965 Scrapped (1966)
21 61233 1963 1966 Scrapped (1966)
22 61252 1963 1964 Scrapped (1966)
23 61300 1963 1965 Scrapped (1966)
24 (1st) 61323 1963 1963 Scrapped (1964)
24 (2nd) 61375 1963 1966 Scrapped (1966)
25 61272 1965 1966 Scrapped (1966)
26 61138 1965 1967 Scrapped (1968)
27 61105 1965 1966 Scrapped (1966)
28 61194 1965 1966 Scrapped (1966)
29 61264 1965 1967 Woodham Brothers , later preserved
30 61050 1966 1968 Scrapped (1968)
31 (2nd) 61051 1966 1966 Scrapped (1966)

Question: Under the LNER Thompson Class B1, what is the oldest BR number?

Question: Give total of previous BR number for number 21 under LNER Thompson Class B1?