的士數
第
  
    
      
        n
      
    
    {\displaystyle n}
  個計程車數（Taxicab number），一般寫作
  
    
      
        Ta
        ⁡
        (n)
      
    
    {\displaystyle \operatorname {Ta} (n)}
  或
  
    
      
        Taxicab
        ⁡
        (n)
      
    
    {\displaystyle \operatorname {Taxicab} (n)}
  ，定義為最小的數能以
  
    
      
        n
      
    
    {\displaystyle n}
  個不同的方法表示成兩個正立方數之和。1938 年，G・H・哈代與愛德華・梅特蘭・賴特證明對於所有正整數
  
    
      
        n
      
    
    {\displaystyle n}
  這樣的數也存在。可是他們的證明對找尋計程車數毫無幫助，截止現時，只找到 6 個計程車數（ A011541）：

  
    
      
        
          
            
              
                Ta
                ⁡
                (1)
                =
                2
              
              
                
                =
                
                  1
                  
                    3
                  
                
                +
                
                  1
                  
                    3
                  
                
              
            
          
        
      
    
    {\displaystyle {\begin {aligned}\operatorname {Ta} (1)=2&=1^{3}+1^{3}\end {aligned}}}
  
  
    
      
        
          
            
              
                Ta
                ⁡
                (2)
                =
                1729
              
              
                
                =
                
                  1
                  
                    3
                  
                
                +
                
                  12
                  
                    3
                  
                
              
            
            
              
              
                
                =
                
                  9
                  
                    3
                  
                
                +
                
                  10
                  
                    3
                  
                
              
            
          
        
      
    
    {\displaystyle {\begin {aligned}\operatorname {Ta} (2)=1729&=1^{3}+12^{3}\\&=9^{3}+10^{3}\end {aligned}}}
  
  
    
      
        
          
            
              
                Ta
                ⁡
                (3)
                =
                87539319
              
              
                
                =
                
                  167
                  
                    3
                  
                
                +
                
                  436
                  
                    3
                  
                
              
            
            
              
              
                
                =
                
                  228
                  
                    3
                  
                
                +
                
                  423
                  
                    3
                  
                
              
            
            
              
              
                
                =
                
                  255
                  
                    3
                  
                
                +
                
                  414
                  
                    3
                  
                
              
            
          
        
      
    
    {\displaystyle {\begin {aligned}\operatorname {Ta} (3)=87539319&=167^{3}+436^{3}\\&=228^{3}+423^{3}\\&=255^{3}+414^{3}\end {aligned}}}
  
  
    
      
        
          
            
              
                Ta
                ⁡
                (4)
                =
                6963472309248
              
              
                
                =
                
                  2421
                  
                    3
                  
                
                +
                
                  19083
                  
                    3
                  
                
              
            
            
              
              
                
                =
                
                  5436
                  
                    3
                  
                
                +
                
                  18948
                  
                    3
                  
                
              
            
            
              
              
                
                =
                
                  10200
                  
                    3
                  
                
                +
                
                  18072
                  
                    3
                  
                
              
            
            
              
              
                
                =
                
                  13322
                  
                    3
                  
                
                +
                
                  16630
                  
                    3
                  
                
              
            
          
        
      
    
    {\displaystyle {\begin {aligned}\operatorname {Ta} (4)=6963472309248&=2421^{3}+19083^{3}\\&=5436^{3}+18948^{3}\\&=10200^{3}+18072^{3}\\&=13322^{3}+16630^{3}\end {aligned}}}
  
  
    
      
        
          
            
              
                Ta
                ⁡
                (5)
                =
                48988659276962496
              
              
                
                =
                
                  38787
                  
                    3
                  
                
                +
                
                  365757
                  
                    3
                  
                
              
            
            
              
              
                
                =
                
                  107839
                  
                    3
                  
                
                +
                
                  362753
                  
                    3
                  
                
              
            
            
              
              
                
                =
                
                  205292
                  
                    3
                  
                
                +
                
                  342952
                  
                    3
                  
                
              
            
            
              
              
                
                =
                
                  221424
                  
                    3
                  
                
                +
                
                  336588
                  
                    3
                  
                
              
            
            
              
              
                
                =
                
                  231518
                  
                    3
                  
                
                +
                
                  331954
                  
                    3
                  
                
              
            
          
        
      
    
    {\displaystyle {\begin {aligned}\operatorname {Ta} (5)=48988659276962496&=38787^{3}+365757^{3}\\&=107839^{3}+362753^{3}\\&=205292^{3}+342952^{3}\\&=221424^{3}+336588^{3}\\&=231518^{3}+331954^{3}\end {aligned}}}
  
  
    
      
        
          
            
              
                Ta
                ⁡
                (6)
                =
                24153319581254312065344
              
              
                
                =
                
                  582162
                  
                    3
                  
                
                +
                
                  28906206
                  
                    3
                  
                
              
            
            
              
              
                
                =
                
                  3064173
                  
                    3
                  
                
                +
                
                  28894803
                  
                    3
                  
                
              
            
            
              
              
                
                =
                
                  8519281
                  
                    3
                  
                
                +
                
                  28657487
                  
                    3
                  
                
              
            
            
              
              
                
                =
                
                  16218068
                  
                    3
                  
                
                +
                
                  27093208
                  
                    3
                  
                
              
            
            
              
              
                
                =
                
                  17492496
                  
                    3
                  
                
                +
                
                  26590452
                  
                    3
                  
                
              
            
            
              
              
                
                =
                
                  18289922
                  
                    3
                  
                
                +
                
                  26224366
                  
                    3
                  
                
              
            
          
        
      
    
    {\displaystyle {\begin {aligned}\operatorname {Ta} (6)=24153319581254312065344&=582162^{3}+28906206^{3}\\&=3064173^{3}+28894803^{3}\\&=8519281^{3}+28657487^{3}\\&=16218068^{3}+27093208^{3}\\&=17492496^{3}+26590452^{3}\\&=18289922^{3}+26224366^{3}\end {aligned}}}
  
  
    
      
        Ta
        ⁡
        (2)
      
    
    {\displaystyle \operatorname {Ta} (2)}
  因為哈代和拉馬努金的故事而為人所知：

在
  
    
      
        Ta
        ⁡
        (2)
      
    
    {\displaystyle \operatorname {Ta} (2)}
  之後，所有的計程車數均用電腦來尋找。