Score
0
Best
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Six numbers, one missing next term. Spot the rule behind each series — steady steps, doubling, growing gaps, Fibonacci sums, alternating operations, squares and cubes — and type the next number before the two-minute clock runs out. The rules get trickier as your score climbs.
Each round shows six numbers in a row followed by a question mark. The numbers follow one hidden rule, and your job is to work out the number that comes next.
Type your answer on the keypad below the row. The ± key flips the sign for the rare series that runs into negative numbers, and ⌫ deletes the last digit. Press OK to submit.
A right answer scores one point and shows the rule, then a new series appears straight away. A wrong answer costs eight seconds from the clock, and the correct number and its rule are shown for a moment before the next series.
You have two minutes in total. Early series use simple steps like +4 or ×2; after a few correct answers you start meeting growing gaps and interleaved series, then Fibonacci-style sums, mixed operations and powers. The game ends when the clock reaches zero.
Start with the differences. Subtract each number from the one after it and look at that new row: if it is constant you have a steady step, if it grows by the same amount each time you have a quadratic series, and if the differences themselves double or triple you are looking at a sum of powers.
If the differences zigzag, try splitting the series into odd and even positions. Interleaved series hide two simple progressions, one climbing and one falling, and each half alone is easy. Alternating operations such as “+3, ×2” also produce a zigzag in the differences, but there the ratio between neighbours jumps back and forth.
When the numbers explode quickly, compare ratios instead of differences. A clean ratio means pure multiplication; a ratio that is almost 2 or 3 but slightly off usually means “multiply, then add or subtract a small constant”. Numbers like 9, 16, 25, 36 or 8, 27, 64 are squares and cubes, sometimes shifted by one or two.
The eight-second penalty is harsh, so a quick guess only pays off if you are fairly sure. If a series looks strange, check whether each term is the sum of the two before it — Fibonacci-style series look irregular until you add neighbours together.