Question 1103160
Can do this on a spreadsheet where
p(2) not is (364/365)
P(3) not is (364/365)(363/365)
p(22) not (1/365)^21*(364*363*...*341)
Here, when not is less than 10% the probability of yes will be greater than or equal to 90%.
n=41
On a calculator, can do 365*364*363*... to about 345, then divide by 365^21.  That will keep it from overloading.  Then repeat, and when 326 changes to 325, it will be <10% or >=90%.