The quiz shows 10 number sequences, one at a time. Each sequence follows one rule. Find the rule and type the next number.
You get one answer for each sequence. A wrong answer shows the correct number, then the next sequence appears. The end screen lists every sequence with its rule. The sequences get harder as you go: sequence 1 is "add 3", sequence 10 is two sequences that take turns. Each level draws from several rules, so the next run gives you different sequences.
How to play
The clock starts at your first keystroke and counts up. There is no time limit.
Sequences come one at a time, in order. You cannot skip a sequence.
Type the next number, then press Enter. The answer commits only on Enter.
You get one answer per sequence. A wrong answer shows the correct number, then the quiz moves on. The rule waits for the end screen.
Your score is the number of sequences you continued correctly, out of 10. A tie ranks by time.
Give up ends the run early and shows your results.
Select "Review answers" on the result screen to see each sequence you played, with its rule.
What counts in this quiz
10 sequences per run, freshly generated each run. Every level holds three or more rules and picks one at random, so a second run is not the same. Every rule uses whole numbers only.
Level 1: one small step, up or down. Level 2: the same step with bigger numbers. Level 3: multiply or divide by the same number. Level 4: the square numbers. Level 5: the gap changes by the same amount each time.
Level 6: each number comes from the numbers before it. Level 7: two rules take turns, such as add 3, then double. Level 8: a family of numbers, such as the primes, the cubes or the factorials. Level 9: one rule with two steps, such as multiply then add. Level 10: two sequences that take turns, or three rules that take turns.
What's not included, and why
No sequence has two valid answers. The quiz tests every sequence against the other rules a player could read into the numbers, and throws the sequence away if a second rule gives a different next number.
No letters, no dates, no trick questions. Every sequence is a rule on whole numbers.
Good to know
The Fibonacci sequence appears in a 1202 book on arithmetic, in a puzzle about breeding rabbits. Indian scholars had described it centuries earlier in the study of poetic metre.
The On-Line Encyclopedia of Integer Sequences holds more than 370,000 sequences. Type a few numbers into it and it names the rule.