### Top Discussions

### Top Discussions

### Popular Groups

PS428106 deals

Xbox One58415 deals

Make Up4884 deals

Nintendo Switch2330 deals

TV41651 deals

PC42454 deals

Laptop28916 deals

iPhone31769 deals

Tablet17894 deals

Shoes11238 deals

Camera19644 deals

Headphones11218 deals

Perfume15070 deals

Watch17057 deals

Toys22951 deals

Lego17033 deals

Dyson2252 deals

Washing Machine8017 deals

Sim Only3322 deals

Car Lease1435 deals

That would be 5+4 =9

My bad, added 4 to 7.

Yep.

To Ollie's original question - no, they can't all be prime, as exactly one of {a,a+2,a+4} must be divisible by 3.

To see this, do you understand modular arithmetic?

If a ≡ 0 (mod 3), then it's divisible by 3 and hence not prime.

If a ≡ 1 (mod 3), then (a + 2) ≡ 0 (mod 3) and hence is not prime

If a ≡ 2 (mod 3), then (a + 1) ≡ 0 (mod 3) and hence is not prime

If the above doesn't make sense, let me know.

I'm hopng that we're not just doing your homework for you?

Edited by:"Illusionary" 2nd Apri will leave it there for my stupidity

in my head it went 17 19 23 haha

Edited by:"pinkleponkle" 2nd AprThen a + 4 = 21 = 3 × 7

Edited by:"Illusionary" 2nd AprIf you add 2 it will probably make it divisible by 3 and if not the it will be divisible by 5.

A=7 9 11 9/3

A=11 13 15 15/5

A=9 11 13 9/3

A= 13 15 17 15/3 or 5

All primes can’t be even after 2 and cannot end with 5 or 0.

Divisibility by 5 is a red herring, but considering divisibility by 3 is indeed the way to go. See my post above for a full explanation.

Therefore if A+2 is odd, A, A+2 and A+4 are 3 consecutive odd numbers. Out of 3 consecutive odd numbers one will always be divisible by 3.

Where A>3 it eliminates 1,3,5 and 3,5,7 which are the only 2 exceptions.

Yep - just make sure that you understand how to prove your assertion about three consutive odd numbers.