n=   r=   letters digits
    option   ,'s
  nPr   nCr   words   Powset   Binomial Coeff      
second space   Plus   Minus   Times   r=  
  nPr   nCr   words   Powset   Binomial Coeff      
advanced functions
P(X) =  
regex to exclude
regex to include  
starts with 3 or ends with 4 or 5: (^3|4$|5$)