Dyalog APL, 11 bytes
2 bytes saved thanks to @ZacharyT
⊣-⍨⊢*1+∘⌊⍟⍨
Takes n as left argument and b as right argument.
Calculates b⌊logbn + 1⌋ - n.
Uriel
- 13.2k
- 4
- 17
- 45