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 and the rule, then the next sequence appears. The sequences get harder as you go: sequence 1 is "add 3", sequence 10 is two sequences that take turns.
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 and the rule, then the quiz moves on.
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.
What counts in this quiz
10 sequences per run, freshly generated each run. Every rule uses whole numbers only.
Level 1: add a constant. Level 2: subtract a constant. Level 3: multiply by 2 or 3. Level 4: the square numbers, sometimes shifted. Level 5: the gap between numbers grows each time.
Level 6: each number is the sum of the two before it. Level 7: two rules take turns, such as add 3, then double. Level 8: the prime numbers or the cube numbers. Level 9: multiply then add, or the triangular numbers. Level 10: two sequences that take turns, n × (n + 1), or multiply then subtract.
What's not included — and why
No sequence has two valid answers. Each rule is checked so the next number is fixed.
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.