1, 3, 9 and 27 kg.

1 kg: 1 on the LHS, ice cream on the RHS.

2kg: 3 on the LHS, 1 and the ice cream on the RHS.

3kg: 3 on the LHS, ice cream on the RHS.

4kg: 3 and 1 on the LHS ...

5kg: 9 on the LHS, 3 and 1 on the RHS

6kg: 9 on the LHS, 6 on the RHS

And so on.

It's a thinly-disguised way of interpreting numbers in base 3.