Thread: is it possible View Single Post
2020-07-14, 08:13   #12
JeppeSN

"Jeppe"
Jan 2016
Denmark

2×83 Posts

Quote:
 Originally Posted by drmurat I asked it because if 2^(n) + 1 is prime and 2^(n+1) + 1 can be prime . it means (2^n) * (2^ (2n) + 1) *(2^ (2n+1) + 1) gives perfect number but it is impossible . one of them is devided by 3
It is true that one of them is divisible by 3. Modulo 3, we have 2^n + 1 ≡ (-1)^n + 1, so every second n produces zero modulo 3.

As mentioned above, n=0 and n=1 both work, because 2^0+1; 2^1+1; 2^2+1 gives 2; 3; 5. For n=0 your formula does make a perfect number, but for n=1, the way I read it, your formula gives 90, which is not perfect.

/JeppeSN