NS-017

Find the next number: 1, 11, 15, 25, 29, ?

Rule: The pattern alternates: +10, +4, +10, +4, ... so the next step is +10.

So the next number is 39.

• Picking the first pattern you see without checking it against all rows/columns.
• Ignoring the simplest rule (counts, rotations, alternations) and jumping to a complex story.
• Not testing your rule on the middle row/column (where many puzzles “break” bad rules).