{\displaystyle \sum _{k=0}^{\infty }{\frac {1}{n^{k}}}=1+{\frac {1}{n-1}}\quad {\mbox{for all}}\quad n\in \mathbb {R} >1.} A Cantor space is a topological space 
  
    
      
        
          2
          
            
              N
            
          
        
      
    
    {\displaystyle 2^{\mathbb {N} }}
   homeomorphic to the Cantor set. The countably infinite product topology of the simplest discrete two-point space, {0, 1}, is the traditional elementary example. The sum of the reciprocals of all non-zero triangular numbers converges to 
  
    
      
        2
      
    
    {\displaystyle 2}
  .Powers of two are central to the concept of Mersenne primes, and important to computer science. Two is the first Mersenne prime exponent.
AKI can be diagnosed if any one of the following is present:

Increase in SCr by ≥0.3 mg/dl (≥26.5 μmol/L) within 48 hours; or
Increase in SCr to ≥1.5 times baseline, which has occurred within the prior 7 days; or
Urine volume < 0.5 mL/kg/h for 6 hours. Staging
The RIFLE criteria, proposed by the Acute Dialysis Quality Initiative (ADQI) group, aid in assessment of the severity of a persons acute kidney injury. The acronym RIFLE is used to define the spectrum of progressive kidney injury seen in AKI:

Risk: 1.5-fold increase in the serum creatinine, or glomerular filtration rate (GFR) decrease by 25 percent, or urine output <0.5 mL/kg per hour for six hours. Injury: Two-fold increase in the serum creatinine, or GFR decrease by 50 percent, or urine output <0.5 mL/kg per hour for 12 hours. Failure: Three-fold increase in the serum creatinine, or GFR decrease by 75 percent, or urine output of <0.3 mL/kg per hour for 24 hours, or no urine output (anuria) for 12 hours. Loss: Complete loss of kidney function (e.g., need for renal replacement therapy) for more than four weeks. End-stage kidney disease: Complete loss of kidney function (e.g., need for renal replacement therapy) for more than three months. Evaluation
The deterioration of kidney function may be signaled by a measurable decrease in urine output. Often, it is diagnosed on the basis of blood tests for substances normally eliminated by the kidney: urea and creatinine. Additionally, the ratio of BUN to creatinine is used to evaluate kidney injury. Both tests have their disadvantages.