Sujiko is the first incarnation of Suko, created by Jai Gomer of Kobayaashi Studios.
The puzzle is tiny, occupying a 3x3 grid. A circled number clue at the centre of each quadrant tells you the sum of the four numbers in that quadrant. The numbers 1-9 must be placed in the grid, in accordance with the circled clues, to complete the puzzle. Occasionally, starter digits are provided.
Sujiko is more challenging than Suko, because there are fewer clues. Strategies can be deployed (see the further details for hints) and yet these usually involve quite advanced thinking, at least in terms of puzzle theory. The puzzle will be familiar to all Sudokulists.
The puzzle is featured in a national daily newspaper.