I, personally, would not worry about this.
For one thing, little kids can be weird.
It's perfectly normal.
For another thing, how many 4 year olds know what pi is?
If she knows it irritates you, she will likely do it more.
People have started noticing and asking questions? So what?
When my daughter was 3, her favorite thing to say was cardiopulmonary resuscitation. She thought it was great fun for us to practice CPR.
Also, she loved to sing.....
"2.54 centimeter worm, 2.54 centimeter worm, measuring the marigolds, seems to me you'd stop to see how beautiful they are."
2.54 centimeters equals an inch. If anyone ever said anything, it was usually, "What little kid knows that stuff?"
It may seem repetitive to you, but I can promise she'll never forget what pi is. Maybe have your husband take it a step further and show her how to use it in an equation. Maybe she's got a love and a knack for numbers and will be a mathemetician. Or a wealthy accountant.
Maybe she's just being 4 and has found something she likes to repeat.
Listen, I was a weird little kid. I admit it.
For instance, I used to walk around in public with my eyes half shut because I thought people would think I was Chinese. I vividly remember it. I never thought for a second my blonde hair would give me away.
It probably drove my mother crazy, but she never said anything and I grew out of it. She didn't call the doctor to find out what was wrong with me.
She did follow my school's recommendation to have me tested and as it turned out, I was a "gifted" child.
I have no doubt there were days my mother wished I wasn't.
:)
Believe it or not, I turned out pretty "normal" with "normal" little weird kids of my own.
I wouldn't worry too much about it at this point.
Just my opinion.