The sums of the first five non-primes greater than zero 
  
    
      
        1
      
    
    {\displaystyle 1}
   + 
  
    
      
        4
      
    
    {\displaystyle 4}
   + 
  
    
      
        6
      
    
    {\displaystyle 6}
   + 
  
    
      
        8
      
    
    {\displaystyle 8}
   + 
  
    
      
        9
      
    
    {\displaystyle 9}
   and the first five prime numbers 
  
    
      
        2
      
    
    {\displaystyle 2}
   + 
  
    
      
        3
      
    
    {\displaystyle 3}
   + 
  
    
      
        5
      
    
    {\displaystyle 5}
   + 
  
    
      
        7
      
    
    {\displaystyle 7}
   + 
  
    
      
        11
      
    
    {\displaystyle 11}
   both equal 
  
    
      
        28
      
    
    {\displaystyle 28}
  ; the 7th triangular number and like 
  
    
      
        6
      
    
    {\displaystyle 6}
   a perfect number, which also includes 
  
    
      
        496
      
    
    {\displaystyle 496}
  , the 31st triangular number and perfect number of the form 
  
    
      
        
          2
          
            p
          
        
      
    
    {\displaystyle 2^{p}}
  −1(
  
    
      
        
          2
          
            p
          
        
      
    
    {\displaystyle 2^{p}}
   − 
  
    
      
        1
      
    
    {\displaystyle 1}
  ) with a 
  
    
      
        p
      
    
    {\displaystyle p}
   of 
  
    
      
        5
      
    
    {\displaystyle 5}
  , by the Euclid–Euler theorem.There are a total of five known unitary perfect numbers, which are numbers that are the sums of their positive proper unitary divisors.
See also
Five Families
Five Nations (disambiguation)
555 (number)
List of highways numbered 5

References
Wells, D. The Penguin Dictionary of Curious and Interesting Numbers London: Penguin Group. (1987): 58–67

External links
 Media related to 5 (number) at Wikimedia Commons
 The dictionary definition of five at Wiktionary
The Number 5
The Positive Integer 5
Prime curiosities: 5