lean_workbook_plus_72093

For a positive integer $n$ , an $n$-sequence is a sequence $(a_0,\ldots,a_n)$ of non-negative integers satisfying the following condition: if $i$ and $j$ are non-negative integers with $i+j \leqslant n$ , then $a_i+a_j \leqslant n$ and $a_{a_i+a_j}=a_{i+j}$ .