An integer sequence $a_1,a_2,\ldots,a_n$ has $a_1=0$, $a_n\leq 10$ and $a_{i+1}-a_i\geq 2$ for $1\leq i<n$.  How many possibilities are there for this sequence?  The sequence may be of any length.

Let's think step by step and output the final answer within \boxed{}.
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