# Simple riddle

#### arcnets

Hi, I'm the guy formerly known as carsten. This is just a test to see if everything works.
OK, you have the numbers
1 2 3 4 5 6 7 8 9 0.
You may insert some + signs and one = sign so to make a valid equation.
Like
12+34+5+6+78=90 (oops, false! )

Happy posting, and a big thanks to Greg who does a great job IMO.

#### Mulder

Easy ..
1+2+3+4+5+67+8=90

#### arcnets

Yes. There's more solutions.

#### drag

1 + 2 + 3 + 4 + 56 + 7 + 8 + 9 = 90
12 + 3 + 45 + 6 + 7 + 8 + 9 = 90

#### Njorl

You used the 9's twice drag.

12+3+4+56+7+8=90
1+23+45+6+7+8=90
nothing =890
nothing=7890
etc.

Njorl

#### Njorl

If 2n-1 is prime, what can you say about (2n-1)*(2n-1)?

Njorl

Perfect!

#### Njorl

Absolutely. I thought that would take longer.

Njorl

#### Njorl

A perfect number is equal to the sum of its factors. For this purpose, 1 is considered a factor, but the number itself is not.

Factors of 6 are 1,2,3 1+2+3=6
Factors of 28 are 1,2,4,7,14 1+2+4+7+14=28

6 and 28 are perfect.

Njorl

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