Puzzle from 1965 Soviet Magazine

Юный Техник 1965 Issue 9 Page 10
### Cube Puzzle
> The game "Cube Puzzle for All" is well known to many children. The task is to build a set of puzzle-figures from seven block elements as shown on the picture. In total there are 27 smaller cubes. There are 11 thousand ways to assemble the simplest of these figures - a cube, but it can be hard to do for many.
> Try to find mathematically to which of seven elements would belong the small cube in the center of the assembled cube. It does not d