8125
Smallest natural number that can be obtained as sum of two square numbers in five different ways:
 
8125 = 5^2 + 90^2 = 27^2 + 86^2 = 30^2 + 85^2 = 50^2 + 75^2 = 58^2 + 69^2
 
 
more interesting 4-digit numbers:  
 
(background-color: #008125)