← back to the spiralPrime factorisation
2
primeA prime number is a whole number greater than 1 whose only divisors are 1 and itself — the indivisible building block of every other number.
Learn more →Prime factorisationEvery whole number above 1 splits into a product of primes in exactly one way — its prime factorisation.
Learn more →
Every whole number above 1 splits into a product of primes in exactly one way — its prime factorisation.
Learn more →2 = 2
2
parity
even
digits
1
digit sum
The digit sum just adds up the digits — handy for divisibility tricks (a number is divisible by 3 exactly when its digit sum is).
2
divisors τ
τ (tau) counts how many positive divisors a number has, including 1 and itself.
Learn more →2
sum of divisors σ
σ (sigma) is the sum of all positive divisors of a number, including 1 and itself.
Learn more →3
classification
Compare a number to the sum of its proper divisors: equal means perfect, more means abundant, less means deficient.
Learn more →deficient