Find a3a_3a3 if an=an−1+an−2+an−3a_n = a_{n-1} + a_{n-2} + a_{n-3}an=an−1+an−2+an−3 with a0=0,a1=1,a2=1a_0=0, a_1=1, a_2=1a0=0,a1=1,a2=1.
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