alchemy set 2. Puzzle 5 - the prequel

Any clue type throughout the set may appear only once. Normal 6x6 sudoku rules apply. Place the digits 1-6 once each in every row, column and 2x3 box. Any Domino in the grid may not be consecutive. Each digit in the grid represents the height of a building in its cell. Taller buildings obstruct the view of shorter ones behind them. Clues outside the grid give the number of buildings visible from that vantage point in the clue's row or column. Digits along a grey line must form a sequence with the digits having a constant distance. i.e. 135 or 333 would work. Cells separated by a white dot has a difference of 3.