Whereas 5 is unique in the Fibonacci sequence, in the Perrin sequence 5 is both the fifth and sixth Perrin numbers.5 is the third Mersenne prime exponent of the form 
  
    
      
        
          2
          
            n
          
        
      
    
    {\displaystyle 2^{n}}
   − 
  
    
      
        1
      
    
    {\displaystyle 1}
  , which yields 
  
    
      
        31
      
    
    {\displaystyle 31}
  : the prime index of the third Mersenne prime and second double Mersenne prime 127, as well as the third double Mersenne prime exponent for the number 2,147,483,647, which is the largest value that a signed 32-bit integer field can hold.
Road rash is a colloquial term for skin injury caused by abrasion with road surfaces, often as a consequence of cycling and motorcycling accidents. It may also result from running, inline skating, roller skating, skateboarding, and longboarding accidents. The term may be applied to both a fresh injury and also to the scar tissue left by an old injury. Symptoms may include pain and heavy bleeding. Motorcyclists can reduce the risks of road rash by wearing appropriate motorcycle personal protective equipment such as a full face helmet, protective clothing, gloves, dusters and boots. Similarly, inline skaters can reduce their chance of such abrasion injuries by wearing protective knee and elbow pads. Road rash is often termed gravel rash in the United Kingdom. The term is old and is mentioned in Rudyard Kiplings Kim (1901). According to the OED it first appeared in print in the Hottens Dictionary of Modern Slang, Cant, and Vulgar Words (2nd Ed, 1860). References
External links

Abrasions and Road rash
Road rash - abrasion treatment