Question 948305
<pre>
  4 = 1×2²
 18 = 2×3²
  ?  
100 = 4×5²
180 = 5×6²   
294 = 6×7²

So obviously, to fill in the missing number:

  4 = 1×2²
 18 = 2×3²
<b><font color="red"> 48 = 3×4²</b></font>
100 = 4×5²
180 = 5×6²   
294 = 6×7²
100 = 4×5²
180 = 5×6²   
294 = 6×7²

Edwin</pre>