Are numerical prayers dangerous?

Dear God, we pray for (insert number) to show up tonight...
Dear God, we pray to grow by (insert number) over the next year...

Should you pray humerical prayers?
Are they healthy?

Frankly, I don't know the answer.
But I think the question should be asked.

For everyone attached to a ministry or event, paid or unpaid, has uttered these prayers in desperation.

And, sometimes, they seemingly pay off.
At other times they don't.

I've been involved in ministries which have both grown and shrunk.
I've been involved in events when vastly more people have turned up than we've expected and an event where only one kid attended. 

Just one.

In a sign of weakness, these types of prayers make me nervous because they are specific enough for a definite success or failure.
With a numerical prayer, either you hit or exceede your number or you don't.

But I think something more alarming can be displayed by a numerical prayer - the heart of the person praying.

Why do they want "that" number?

Do they want to look successful?
Do they need to reach a threshold to be financially viable?
Have they been given a numerical ultimatum to reach in order to be vocationally secure?

Or, do they want "that" number because each one represents an individual who needs Jesus?

I ask the last question because, if that's the genuine aim, then why does reaching "that" number matter?