To find cube of number just above 100 :
A cube will have 3 parts. Let us take an example to find 1043.
Part I -> 104 is 4 more than 100, so add thrice of this 4 i.e. 12 to 100 to get 112.
part II -> multiply that 12 we got in I part to 4 (the more part from 100) to get 48.
part III -> cube of 4 (the more part of 100) to get 64.
Append three parts to get 112 48 64 i.e. 1124864 is cube of 104.

Note : Part II and III must contain only 2 digits since there are 2 zeros in 100.

Let us take another example : 1083
Part I -> 8 more than 100, so add 3*8 to 100 to get 124.
Part II -> 24*8 = 192
Part III -> 83 = 512.
So 1083 = 124 192 512, but here part II and III have extra digits so from right to left, we keep shifting to left.
So add 5 of 512 to 192 to get 197.
Then add 1 of 197 to 124 to get 125.
So 1083 = 125 97 12

Let us take another example : 1013
Part I -> 1 more than 100, so add 3*1 to 100 to get 103.
Part II -> 3*1 = 3, but we require 2 digits so it becomes 03
Part III -> 13 = 1 = 01
So 1013 = 103 03 01

Similarly we can do this for base 1000, but now part II and III contains 3 digits.
Let us take an example : 10043
Part I -> 4 more than 1000, so add 3*4 to 1000 to get 1012.
Part II -> 12*4 = 48 = 048
Part III -> 43 = 64 = 064.
So 10043 = 1012 048 064