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Prime numbers can be used for an exploring numbers type starter.

Find numbers with exactly two factors. Three factors? (A square of a prime number). Four? (A product of two different prime numbers). **Five**? Or **generalise** (perhaps rather too long for a starter!)

All prime numbers >3 are either one more or one less than a multiple of 6.

Proof : Primes 6k+1 6k-1 proof

For further ideas see **these possibilities from Nrich**. Two Primes Make One Square or Penta Primes for example could make suitable starters.

Try some of these ideas from **Murderous Maths**.

This **application from Ptolemy.co.uk **by Alec McEachran provides an excellent visualisation of the prime factorisation of a number. The author has written about the application **in his own blog**.

Enter your own number using this part of the display:

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