Sum of 4 first index $\sum_{n=1}^4a_i=1$

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$\sum_{n=1}^4a_i=1$ The meaning of this sum, means that:
*$a_1=1, a_2=1, a_3=1, a_4=1$
OR:
*$a_1=1, a_2=2, a_3=3, a_4=6$

Or something else?