Hanidoku
It's an interesting and challenging variant of Sudoku where you place the numbers 1-9 in a grid. This grid is shaped like a honeycomb. Instead of nine rows, nine columns and nine blocks, it has nine rows, nine inclining lines and nine declining lines. Each row, decline and incline, must contain unique numbers. But, because each line is not 9 cells in length, they do not call contain the digits 1-9. If there is less than 9 cells, the numbers must be consecutive in that line: this is the interesting difference in Hanidoku!! For example, a line of length 7 can only contain numbers 1,2,3,4,5,6,7 or 2,3,4,5,6,7,8 or 3,4,5,6,7,8,9.