21105+4742
- Unique Name: 21105+4742BU 159AB
- RA: 21 10 30.96
- Dec: +47 41 32.0
- Discoverer: BU
- Discoverer Number: 159
- Components: AB
- First year: 1873
- Last year: 2011
- Observations: 25
- First position angle: 330
- Last position angle: 312
- First separation: 1.2
- Last separation: 1.2
- Mag first component: 6.55
- Mag second component: 9.07
- Spectral type: B6IV
- Primary proper motion RA: -4
- Primary proper motion DEC: 1
- Secondary proper motion RA: -4
- Secondary proper motion DEC: 1
- Durchmusterung: +47 3322
- Notes: N