Renban

Renban is a Sudoku-like logic puzzle. The goal is to enter a consecutive number sequence (usually from 1 to the block size) in each block.

Rules: In each cell of the NxN grid, enter a number in the range 1–N. Each number must appear exactly once in each row and column.
No number may occur more than once in a block. The numbers in a block must form a continuous sequence, but not necessarily in the natural order (4-5-6 or 1-2-3 are allowed, 3-4-6 is not).