Quote:

Originally Posted by **nimesh**
Shabbir: I would like to highlight something here.

__As per the rules:__

Added 19th Jun 2009 - You can post as many answers as you like, but only your last posted answer will be considered.

Mridula posted multiple answers and you said that his first reply **137** is the right answer

So... now what???

What say Saswat??

**@shabbir**
Anyway, this question was

**INCORRECT**. So, it should be canceled. (Just another reason)

137 and 173 are

**NOT** the only 3-digit combinations of 1, 3, and 7.

Combinations like 371, 713 and 731 are composite.

And how come the digit '1' is prime ?!?

These were the errors I had noticed and so I asked you, if we had to consider 2-digit and 3-digit combinations too. And then there was a power outage here

for about an hour.

Even if we were to consider only 2-digit combinations ONLY, then also such a number is impossible 'cuz 2, 3, 5, 7 are the only prime digits and if we choose any 3 out of them, we will have to select 2 or 5 or both. But then any 2-digit number of the form X2 or X5 (where X is any digit, in this case 3 or 7), is composite !

So, this question should

**NOT** have the (invalid) 3rd requirement : "Any combination of those digits are also prime".