"have not the least idea"
Hi, I'm an english learner.
Nice to meet you :)
I've got a question about "have not something"

I have not a pen. (x)
I don't have a pen. (o)

I have not the least idea. (o)
I don't have the least idea. (o)

Is that right?
only with "the least idea" I can use "have not something"?
Is there another example?

Question

"have not the least idea"
Hi, I'm an english learner.
Nice to meet you :)
I've got a question about "have not something"

I have not a pen. (x)
I don't have a pen. (o)

I have not the least idea. (o)
I don't have the least idea. (o)

Is that right?
only with "the least idea" I can use "have not something"?
Is there another example?

Answer

"I have not... [noun phrase]" is outdated in English. It is very old.

Today, we say, "I do not (or: don't) have...[noun phrase]".

Therefore: "I don't have a pen."

"I don't have the least idea" might be grammatically correct, but it does not sound natural. It is more common to say "I don't have any idea" or "I don't have the slightest idea" or "I don't have the foggiest idea."

You can also say: "I haven't got the slightest/least idea."

Answer

It would be "I have the least idea" Which just means 'I do not know'. ---------
Another example would be "She hasn't the least interest", which just means 'She has no interest'.