The answer to this is 4=256.
This question tests the basic knowledge of square roots. The numbers 1,2,3 and 4 are considered base numbers and each of these is raised to the power of 4 also denoted by the letter n. This can also be put in a simpler way. All the given numbers are simply quadrupled meaning multiplied by 4.
1*1*1*1=4;
2*2*2*2=16;
3*3*3*3=64;
4*4*4*4=256.