4
x 2 x 3  5 x x x  x x x x  x x x x
x 6 x x  x 2 x x  x 8 x 3  4 x x x
x x x x  x 4 8 x  x x x x  x x x x
x x x x  x x x x  x 2 x x  x x 6 x

x x 8 x  x x 4 x  x x x x  x x x 1
x x 5 x  3 x x x  9 x x 1  6 x x x
x x x x  x x 6 1  x x x x  x x x x
x x 1 9  8 x x x  x x 4 x  x x x x

x x 7 x  x x x x  x x x x  x x x x
2 x x x  6 x x x  3 x 7 x  x x 5 x
x x x x  4 8 x 5  x x x x  x 6 x x
3 x x 8  1 x x x  6 x 9 x  2 x x x

x x 6 x  x x x 8  x x 1 x  x x 2 x
x x x x  x 1 x x  x x x x  x x x x
x x x x  x 3 x x  2 5 x 7  x x x 8
x 4 2 x  x x x 6  8 x x x  x 1 x 5

#t11d3p1
Sudoku 16×16 - Hard
https://sudoku-puzzles.net/sudoku-16x16-hard/

12  2 13  3 ║  5  6 15 16 ║  1  7 10  4 ║  8 11 14  9 
14  6 15 16 ║  9  2 11 12 ║ 13  8  5  3 ║  4  7  1 10 
 5  1  9 10 ║  7  4  8  3 ║ 14 15 11  6 ║ 12  2 13 16 
 8 11  4  7 ║ 10 13  1 14 ║ 16  2 12  9 ║  5 15  6  3 
════════════╬═════════════╬═════════════╬════════════
15 14  8 11 ║ 12 16  4  9 ║  5  6  3  2 ║ 13 10  7  1 
13 16  5 12 ║  3 15 14  7 ║  9 10  8  1 ║  6  4 11  2 
 4  3 10  2 ║ 13  5  6  1 ║  7 11 15 14 ║  9  8 16 12 
 6  7  1  9 ║  8 10  2 11 ║ 12 13  4 16 ║ 14  5  3 15 
════════════╬═════════════╬═════════════╬════════════
 1 13  7  6 ║  2 12  9 15 ║ 10  4 16  5 ║ 11  3  8 14 
 2 15 11  4 ║  6 14 16 10 ║  3 12  7  8 ║  1  9  5 13 
10  9 16 14 ║  4  8  3  5 ║ 11  1  2 13 ║ 15  6 12  7 
 3  5 12  8 ║  1 11  7 13 ║  6 14  9 15 ║  2 16 10  4 
════════════╬═════════════╬═════════════╬════════════
16 12  6 15 ║ 14  9  5  8 ║  4  3  1 10 ║  7 13  2 11 
 7  8  3  5 ║ 16  1 12  2 ║ 15  9 13 11 ║ 10 14  4  6 
11 10 14  1 ║ 15  3 13  4 ║  2  5  6  7 ║ 16 12  9  8 
 9  4  2 13 ║ 11  7 10  6 ║  8 16 14 12 ║  3  1 15  5