Primes, factors, multiples and divisibility — the structure underneath the numbers.
Other topics:
Arithmetic Games Fractions & Percentages Logic & Puzzle Games Number Theory Games Speed & Reflex Games Rare & Unusual Maths
The rules everyone knows
The digit-sum tests
The last-two-digits family
Alternating digit sums
A gentle first grid
The classic range
Where the tricks matter
Thirty seconds, small grid
Targets under 30
Targets to 100
Targets to 200
Ten rounds, mixed sizes
A short first pass
The teaching classic
The full hundred grid
Beyond the hundred square
Every game on YogiCalc is free, runs entirely in your browser, needs no sign-up and saves your best score on your own device. Nothing is uploaded anywhere. They work on a phone, a tablet or a computer.
Looking for something else? The full games library lists all 110 games, and the calculator library covers finance, tax, health and conversion.